diff --git a/demo/rust/src/interface.rs b/demo/rust/src/interface.rs
index 9ad9313..e411a3d 100644
--- a/demo/rust/src/interface.rs
+++ b/demo/rust/src/interface.rs
@@ -40,7 +40,7 @@ where
 pub enum QString {}
 
 fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
-    let utf16 = unsafe { slice::from_raw_parts(str, len as usize) };
+    let utf16 = unsafe { slice::from_raw_parts(str, to_usize(len)) };
     let characters = decode_utf16(utf16.iter().cloned())
         .into_iter()
         .map(|r| r.unwrap());
@@ -65,6 +65,23 @@ pub struct QModelIndex {
     internal_id: usize,
 }
 
+
+fn to_usize(n: c_int) -> usize {
+    if n < 0 {
+        panic!("Cannot cast {} to usize", n);
+    }
+    n as usize
+}
+
+
+fn to_c_int(n: usize) -> c_int {
+    if n > c_int::max_value() as usize {
+        panic!("Cannot cast {} to c_int", n);
+    }
+    n as c_int
+}
+
+
 pub struct DemoQObject {}
 
 #[derive(Clone)]
@@ -436,15 +453,15 @@ pub unsafe extern "C" fn fibonacci_list_free(ptr: *mut FibonacciList) {
 
 #[no_mangle]
 pub unsafe extern "C" fn fibonacci_list_row_count(ptr: *const FibonacciList) -> c_int {
-    (&*ptr).row_count() as c_int
+    to_c_int((&*ptr).row_count())
 }
 #[no_mangle]
 pub unsafe extern "C" fn fibonacci_list_insert_rows(ptr: *mut FibonacciList, row: c_int, count: c_int) -> bool {
-    (&mut *ptr).insert_rows(row as usize, count as usize)
+    (&mut *ptr).insert_rows(to_usize(row), to_usize(count))
 }
 #[no_mangle]
 pub unsafe extern "C" fn fibonacci_list_remove_rows(ptr: *mut FibonacciList, row: c_int, count: c_int) -> bool {
-    (&mut *ptr).remove_rows(row as usize, count as usize)
+    (&mut *ptr).remove_rows(to_usize(row), to_usize(count))
 }
 #[no_mangle]
 pub unsafe extern "C" fn fibonacci_list_can_fetch_more(ptr: *const FibonacciList) -> bool {
@@ -466,13 +483,13 @@ pub unsafe extern "C" fn fibonacci_list_sort(
 #[no_mangle]
 pub extern "C" fn fibonacci_list_data_fibonacci_number(ptr: *const FibonacciList, row: c_int) -> u64 {
     let o = unsafe { &*ptr };
-    o.fibonacci_number(row as usize).into()
+    o.fibonacci_number(to_usize(row)).into()
 }
 
 #[no_mangle]
 pub extern "C" fn fibonacci_list_data_row(ptr: *const FibonacciList, row: c_int) -> u64 {
     let o = unsafe { &*ptr };
-    o.row(row as usize).into()
+    o.row(to_usize(row)).into()
 }
 
 pub struct FileSystemTreeQObject {}
@@ -608,7 +625,7 @@ pub extern "C" fn file_system_tree_path_get(
     let v = o.path();
     if let Some(v) = v {
         let s: *const c_char = v.as_ptr() as (*const c_char);
-        set(p, s, v.len() as c_int);
+        set(p, s, to_c_int(v.len()));
     }
 }
 
@@ -632,11 +649,11 @@ pub unsafe extern "C" fn file_system_tree_row_count(
     item: usize,
     valid: bool,
 ) -> c_int {
-    if valid {
-        (&*ptr).row_count(Some(item)) as c_int
+    to_c_int(if valid {
+        (&*ptr).row_count(Some(item))
     } else {
-        (&*ptr).row_count(None) as c_int
-    }
+        (&*ptr).row_count(None)
+    })
 }
 #[no_mangle]
 pub unsafe extern "C" fn file_system_tree_can_fetch_more(
@@ -674,16 +691,16 @@ pub unsafe extern "C" fn file_system_tree_index(
     row: c_int,
 ) -> usize {
     if !valid {
-        (&*ptr).index(None, row as usize)
+        (&*ptr).index(None, to_usize(row))
     } else {
-        (&*ptr).index(Some(item), row as usize)
+        (&*ptr).index(Some(item), to_usize(row))
     }
 }
 #[no_mangle]
 pub unsafe extern "C" fn file_system_tree_parent(ptr: *const FileSystemTree, index: usize) -> QModelIndex {
     if let Some(parent) = (&*ptr).parent(index) {
         QModelIndex {
-            row: (&*ptr).row(parent) as c_int,
+            row: to_c_int((&*ptr).row(parent)),
             internal_id: parent,
         }
     } else {
@@ -695,7 +712,7 @@ pub unsafe extern "C" fn file_system_tree_parent(ptr: *const FileSystemTree, ind
 }
 #[no_mangle]
 pub unsafe extern "C" fn file_system_tree_row(ptr: *const FileSystemTree, item: usize) -> c_int {
-    (&*ptr).row(item) as c_int
+    to_c_int((&*ptr).row(item))
 }
 
 #[no_mangle]
@@ -707,7 +724,7 @@ pub extern "C" fn file_system_tree_data_file_icon(
     let o = unsafe { &*ptr };
     let data = o.file_icon(item);
     let s: *const c_char = data.as_ptr() as (*const c_char);
-    set(d, s, data.len() as c_int);
+    set(d, s, to_c_int(data.len()));
 }
 
 #[no_mangle]
@@ -719,7 +736,7 @@ pub extern "C" fn file_system_tree_data_file_name(
     let o = unsafe { &*ptr };
     let data = o.file_name(item);
     let s: *const c_char = data.as_ptr() as (*const c_char);
-    set(d, s, data.len() as c_int);
+    set(d, s, to_c_int(data.len()));
 }
 
 #[no_mangle]
@@ -732,7 +749,7 @@ pub extern "C" fn file_system_tree_data_file_path(
     let data = o.file_path(item);
     if let Some(data) = data {
         let s: *const c_char = data.as_ptr() as (*const c_char);
-        set(d, s, data.len() as c_int);
+        set(d, s, to_c_int(data.len()));
     }
 }
 
@@ -894,11 +911,11 @@ pub unsafe extern "C" fn processes_row_count(
     item: usize,
     valid: bool,
 ) -> c_int {
-    if valid {
-        (&*ptr).row_count(Some(item)) as c_int
+    to_c_int(if valid {
+        (&*ptr).row_count(Some(item))
     } else {
-        (&*ptr).row_count(None) as c_int
-    }
+        (&*ptr).row_count(None)
+    })
 }
 #[no_mangle]
 pub unsafe extern "C" fn processes_can_fetch_more(
@@ -936,16 +953,16 @@ pub unsafe extern "C" fn processes_index(
     row: c_int,
 ) -> usize {
     if !valid {
-        (&*ptr).index(None, row as usize)
+        (&*ptr).index(None, to_usize(row))
     } else {
-        (&*ptr).index(Some(item), row as usize)
+        (&*ptr).index(Some(item), to_usize(row))
     }
 }
 #[no_mangle]
 pub unsafe extern "C" fn processes_parent(ptr: *const Processes, index: usize) -> QModelIndex {
     if let Some(parent) = (&*ptr).parent(index) {
         QModelIndex {
-            row: (&*ptr).row(parent) as c_int,
+            row: to_c_int((&*ptr).row(parent)),
             internal_id: parent,
         }
     } else {
@@ -957,7 +974,7 @@ pub unsafe extern "C" fn processes_parent(ptr: *const Processes, index: usize) -
 }
 #[no_mangle]
 pub unsafe extern "C" fn processes_row(ptr: *const Processes, item: usize) -> c_int {
-    (&*ptr).row(item) as c_int
+    to_c_int((&*ptr).row(item))
 }
 
 #[no_mangle]
@@ -969,7 +986,7 @@ pub extern "C" fn processes_data_cmd(
     let o = unsafe { &*ptr };
     let data = o.cmd(item);
     let s: *const c_char = data.as_ptr() as (*const c_char);
-    set(d, s, data.len() as c_int);
+    set(d, s, to_c_int(data.len()));
 }
 
 #[no_mangle]
@@ -999,7 +1016,7 @@ pub extern "C" fn processes_data_name(
     let o = unsafe { &*ptr };
     let data = o.name(item);
     let s: *const c_char = data.as_ptr() as (*const c_char);
-    set(d, s, data.len() as c_int);
+    set(d, s, to_c_int(data.len()));
 }
 
 #[no_mangle]
@@ -1127,15 +1144,15 @@ pub unsafe extern "C" fn time_series_free(ptr: *mut TimeSeries) {
 
 #[no_mangle]
 pub unsafe extern "C" fn time_series_row_count(ptr: *const TimeSeries) -> c_int {
-    (&*ptr).row_count() as c_int
+    to_c_int((&*ptr).row_count())
 }
 #[no_mangle]
 pub unsafe extern "C" fn time_series_insert_rows(ptr: *mut TimeSeries, row: c_int, count: c_int) -> bool {
-    (&mut *ptr).insert_rows(row as usize, count as usize)
+    (&mut *ptr).insert_rows(to_usize(row), to_usize(count))
 }
 #[no_mangle]
 pub unsafe extern "C" fn time_series_remove_rows(ptr: *mut TimeSeries, row: c_int, count: c_int) -> bool {
-    (&mut *ptr).remove_rows(row as usize, count as usize)
+    (&mut *ptr).remove_rows(to_usize(row), to_usize(count))
 }
 #[no_mangle]
 pub unsafe extern "C" fn time_series_can_fetch_more(ptr: *const TimeSeries) -> bool {
@@ -1157,7 +1174,7 @@ pub unsafe extern "C" fn time_series_sort(
 #[no_mangle]
 pub extern "C" fn time_series_data_cos(ptr: *const TimeSeries, row: c_int) -> f32 {
     let o = unsafe { &*ptr };
-    o.cos(row as usize).into()
+    o.cos(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -1165,13 +1182,13 @@ pub unsafe extern "C" fn time_series_set_data_cos(
     ptr: *mut TimeSeries, row: c_int,
     v: f32,
 ) -> bool {
-    (&mut *ptr).set_cos(row as usize, v)
+    (&mut *ptr).set_cos(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn time_series_data_sin(ptr: *const TimeSeries, row: c_int) -> f32 {
     let o = unsafe { &*ptr };
-    o.sin(row as usize).into()
+    o.sin(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -1179,13 +1196,13 @@ pub unsafe extern "C" fn time_series_set_data_sin(
     ptr: *mut TimeSeries, row: c_int,
     v: f32,
 ) -> bool {
-    (&mut *ptr).set_sin(row as usize, v)
+    (&mut *ptr).set_sin(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn time_series_data_time(ptr: *const TimeSeries, row: c_int) -> f32 {
     let o = unsafe { &*ptr };
-    o.time(row as usize).into()
+    o.time(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -1193,5 +1210,5 @@ pub unsafe extern "C" fn time_series_set_data_time(
     ptr: *mut TimeSeries, row: c_int,
     v: f32,
 ) -> bool {
-    (&mut *ptr).set_time(row as usize, v)
+    (&mut *ptr).set_time(to_usize(row), v)
 }
diff --git a/src/rust.cpp b/src/rust.cpp
index 75b233e..1d47e6e 100644
--- a/src/rust.cpp
+++ b/src/rust.cpp
@@ -176,7 +176,7 @@ pub extern "C" fn %1_%2(ptr: *%3 %4)").arg(lcname, lc, f.mut ? "mut" : "const",
             r << "    let mut " << a->name << " = String::new();\n";
             r << QString("    set_string_from_utf16(&mut %1, %1_str, %1_len);\n").arg(a->name);
         } else if (a->type.name == "QByteArray") {
-            r << QString("    let %1 = unsafe { slice::from_raw_parts(%1_str as *const u8, %1_len as usize) };\n").arg(a->name);
+            r << QString("    let %1 = unsafe { slice::from_raw_parts(%1_str as *const u8, to_usize(%1_len)) };\n").arg(a->name);
         }
     }
     if (f.mut) {
@@ -438,7 +438,7 @@ pub extern "C" fn %2_get(
     let o = unsafe { &*ptr };
     let v = o.%3();
     let s: *const c_char = v.as_ptr() as (*const c_char);
-    set(p, s, v.len() as c_int);
+    set(p, s, to_c_int(v.len()));
 }
 )").arg(o.name, base, snakeCase(p.name), p.type.name);
             if (p.write && p.type.name == "QString") {
@@ -456,7 +456,7 @@ pub extern "C" fn %2_set(ptr: *mut %1, v: *const c_ushort, len: c_int) {
 #[no_mangle]
 pub extern "C" fn %2_set(ptr: *mut %1, v: *const c_char, len: c_int) {
     let o = unsafe { &mut *ptr };
-    let v = unsafe { slice::from_raw_parts(v as *const u8, len as usize) };
+    let v = unsafe { slice::from_raw_parts(v as *const u8, to_usize(len)) };
     o.set_%3(v);
 }
 )").arg(o.name, base, snakeCase(p.name));
@@ -473,7 +473,7 @@ pub extern "C" fn %2_get(
     let v = o.%3();
     if let Some(v) = v {
         let s: *const c_char = v.as_ptr() as (*const c_char);
-        set(p, s, v.len() as c_int);
+        set(p, s, to_c_int(v.len()));
     }
 }
 )").arg(o.name, base, snakeCase(p.name), p.type.name);
@@ -492,7 +492,7 @@ pub extern "C" fn %2_set(ptr: *mut %1, v: *const c_ushort, len: c_int) {
 #[no_mangle]
 pub extern "C" fn %2_set(ptr: *mut %1, v: *const c_char, len: c_int) {
     let o = unsafe { &mut *ptr };
-    let v = unsafe { slice::from_raw_parts(v as *const u8, len as usize) };
+    let v = unsafe { slice::from_raw_parts(v as *const u8, to_usize(len)) };
     o.set_%3(Some(v.into()));
 }
 )").arg(o.name, base, snakeCase(p.name));
@@ -548,15 +548,15 @@ pub extern "C" fn %2_set_none(ptr: *mut %1) {
         r << QString(R"(
 #[no_mangle]
 pub unsafe extern "C" fn %2_row_count(ptr: *const %1) -> c_int {
-    (&*ptr).row_count() as c_int
+    to_c_int((&*ptr).row_count())
 }
 #[no_mangle]
 pub unsafe extern "C" fn %2_insert_rows(ptr: *mut %1, row: c_int, count: c_int) -> bool {
-    (&mut *ptr).insert_rows(row as usize, count as usize)
+    (&mut *ptr).insert_rows(to_usize(row), to_usize(count))
 }
 #[no_mangle]
 pub unsafe extern "C" fn %2_remove_rows(ptr: *mut %1, row: c_int, count: c_int) -> bool {
-    (&mut *ptr).remove_rows(row as usize, count as usize)
+    (&mut *ptr).remove_rows(to_usize(row), to_usize(count))
 }
 #[no_mangle]
 pub unsafe extern "C" fn %2_can_fetch_more(ptr: *const %1) -> bool {
@@ -583,11 +583,11 @@ pub unsafe extern "C" fn %2_row_count(
     item: usize,
     valid: bool,
 ) -> c_int {
-    if valid {
-        (&*ptr).row_count(Some(item)) as c_int
+    to_c_int(if valid {
+        (&*ptr).row_count(Some(item))
     } else {
-        (&*ptr).row_count(None) as c_int
-    }
+        (&*ptr).row_count(None)
+    })
 }
 #[no_mangle]
 pub unsafe extern "C" fn %2_can_fetch_more(
@@ -625,16 +625,16 @@ pub unsafe extern "C" fn %2_index(
     row: c_int,
 ) -> usize {
     if !valid {
-        (&*ptr).index(None, row as usize)
+        (&*ptr).index(None, to_usize(row))
     } else {
-        (&*ptr).index(Some(item), row as usize)
+        (&*ptr).index(Some(item), to_usize(row))
     }
 }
 #[no_mangle]
 pub unsafe extern "C" fn %2_parent(ptr: *const %1, index: usize) -> QModelIndex {
     if let Some(parent) = (&*ptr).parent(index) {
         QModelIndex {
-            row: (&*ptr).row(parent) as c_int,
+            row: to_c_int((&*ptr).row(parent)),
             internal_id: parent,
         }
     } else {
@@ -646,13 +646,13 @@ pub unsafe extern "C" fn %2_parent(ptr: *const %1, index: usize) -> QModelIndex
 }
 #[no_mangle]
 pub unsafe extern "C" fn %2_row(ptr: *const %1, item: usize) -> c_int {
-    (&*ptr).row(item) as c_int
+    to_c_int((&*ptr).row(item))
 }
 )").arg(o.name, lcname);
     }
     if (o.type != ObjectType::Object) {
         QString indexDecl = ", row: c_int";
-        QString index = "row as usize";
+        QString index = "to_usize(row)";
         if (o.type == ObjectType::Tree) {
             indexDecl = ", item: usize";
             index = "item";
@@ -669,7 +669,7 @@ pub extern "C" fn %2_data_%3(
     let o = unsafe { &*ptr };
     let data = o.%3(%5);
     let s: *const c_char = data.as_ptr() as (*const c_char);
-    set(d, s, data.len() as c_int);
+    set(d, s, to_c_int(data.len()));
 }
 )").arg(o.name, lcname, snakeCase(ip.name), indexDecl, index, ip.type.name);
             } else if (ip.type.isComplex()) {
@@ -684,7 +684,7 @@ pub extern "C" fn %2_data_%3(
     let data = o.%3(%5);
     if let Some(data) = data {
         let s: *const c_char = data.as_ptr() as (*const c_char);
-        set(d, s, data.len() as c_int);
+        set(d, s, to_c_int(data.len()));
     }
 }
 )").arg(o.name, lcname, snakeCase(ip.name), indexDecl, index, ip.type.name);
@@ -723,7 +723,7 @@ pub extern "C" fn %2_set_data_%3(
     s: *const c_char, len: c_int,
 ) -> bool {
     let o = unsafe { &mut *ptr };
-    let slice = unsafe { ::std::slice::from_raw_parts(s as *const u8, len as usize) };
+    let slice = unsafe { ::std::slice::from_raw_parts(s as *const u8, to_usize(len)) };
     o.set_%3(%5, %6)
 }
 )").arg(o.name, lcname, snakeCase(ip.name), indexDecl, index, ip.optional ?"Some(slice)" :"slice");
@@ -819,7 +819,7 @@ where
 pub enum QString {}
 
 fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
-    let utf16 = unsafe { slice::from_raw_parts(str, len as usize) };
+    let utf16 = unsafe { slice::from_raw_parts(str, to_usize(len)) };
     let characters = decode_utf16(utf16.iter().cloned())
         .into_iter()
         .map(|r| r.unwrap());
@@ -849,6 +849,31 @@ pub struct QModelIndex {
     row: c_int,
     internal_id: usize,
 }
+)";
+    }
+
+    if (hasString || hasByteArray || hasListOrTree) {
+        r << R"(
+
+fn to_usize(n: c_int) -> usize {
+    if n < 0 {
+        panic!("Cannot cast {} to usize", n);
+    }
+    n as usize
+}
+
+)";
+    }
+
+    if (hasString || hasByteArray || hasListOrTree) {
+        r << R"(
+fn to_c_int(n: usize) -> c_int {
+    if n > c_int::max_value() as usize {
+        panic!("Cannot cast {} to c_int", n);
+    }
+    n as c_int
+}
+
 )";
     }
 }
diff --git a/templates/qt_quick/rust/src/interface.rs b/templates/qt_quick/rust/src/interface.rs
index 1a8e317..50503ea 100644
--- a/templates/qt_quick/rust/src/interface.rs
+++ b/templates/qt_quick/rust/src/interface.rs
@@ -14,7 +14,7 @@ use implementation::*;
 pub enum QString {}
 
 fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
-    let utf16 = unsafe { slice::from_raw_parts(str, len as usize) };
+    let utf16 = unsafe { slice::from_raw_parts(str, to_usize(len)) };
     let characters = decode_utf16(utf16.iter().cloned())
         .into_iter()
         .map(|r| r.unwrap());
@@ -23,6 +23,23 @@ fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
 }
 
 
+
+fn to_usize(n: c_int) -> usize {
+    if n < 0 {
+        panic!("Cannot cast {} to usize", n);
+    }
+    n as usize
+}
+
+
+fn to_c_int(n: usize) -> c_int {
+    if n > c_int::max_value() as usize {
+        panic!("Cannot cast {} to c_int", n);
+    }
+    n as c_int
+}
+
+
 pub struct SimpleQObject {}
 
 #[derive(Clone)]
@@ -79,7 +96,7 @@ pub extern "C" fn simple_message_get(
     let o = unsafe { &*ptr };
     let v = o.message();
     let s: *const c_char = v.as_ptr() as (*const c_char);
-    set(p, s, v.len() as c_int);
+    set(p, s, to_c_int(v.len()));
 }
 
 #[no_mangle]
diff --git a/templates/qt_widgets/rust/src/interface.rs b/templates/qt_widgets/rust/src/interface.rs
index 1a8e317..50503ea 100644
--- a/templates/qt_widgets/rust/src/interface.rs
+++ b/templates/qt_widgets/rust/src/interface.rs
@@ -14,7 +14,7 @@ use implementation::*;
 pub enum QString {}
 
 fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
-    let utf16 = unsafe { slice::from_raw_parts(str, len as usize) };
+    let utf16 = unsafe { slice::from_raw_parts(str, to_usize(len)) };
     let characters = decode_utf16(utf16.iter().cloned())
         .into_iter()
         .map(|r| r.unwrap());
@@ -23,6 +23,23 @@ fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
 }
 
 
+
+fn to_usize(n: c_int) -> usize {
+    if n < 0 {
+        panic!("Cannot cast {} to usize", n);
+    }
+    n as usize
+}
+
+
+fn to_c_int(n: usize) -> c_int {
+    if n > c_int::max_value() as usize {
+        panic!("Cannot cast {} to c_int", n);
+    }
+    n as c_int
+}
+
+
 pub struct SimpleQObject {}
 
 #[derive(Clone)]
@@ -79,7 +96,7 @@ pub extern "C" fn simple_message_get(
     let o = unsafe { &*ptr };
     let v = o.message();
     let s: *const c_char = v.as_ptr() as (*const c_char);
-    set(p, s, v.len() as c_int);
+    set(p, s, to_c_int(v.len()));
 }
 
 #[no_mangle]
diff --git a/tests/rust_functions/src/interface.rs b/tests/rust_functions/src/interface.rs
index 1758eb6..a2aed64 100644
--- a/tests/rust_functions/src/interface.rs
+++ b/tests/rust_functions/src/interface.rs
@@ -14,7 +14,7 @@ use implementation::*;
 pub enum QString {}
 
 fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
-    let utf16 = unsafe { slice::from_raw_parts(str, len as usize) };
+    let utf16 = unsafe { slice::from_raw_parts(str, to_usize(len)) };
     let characters = decode_utf16(utf16.iter().cloned())
         .into_iter()
         .map(|r| r.unwrap());
@@ -23,6 +23,23 @@ fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
 }
 
 
+
+fn to_usize(n: c_int) -> usize {
+    if n < 0 {
+        panic!("Cannot cast {} to usize", n);
+    }
+    n as usize
+}
+
+
+fn to_c_int(n: usize) -> c_int {
+    if n > c_int::max_value() as usize {
+        panic!("Cannot cast {} to c_int", n);
+    }
+    n as c_int
+}
+
+
 pub struct PersonQObject {}
 
 #[derive(Clone)]
@@ -85,7 +102,7 @@ pub extern "C" fn person_user_name_get(
     let o = unsafe { &*ptr };
     let v = o.user_name();
     let s: *const c_char = v.as_ptr() as (*const c_char);
-    set(p, s, v.len() as c_int);
+    set(p, s, to_c_int(v.len()));
 }
 
 #[no_mangle]
@@ -136,8 +153,8 @@ pub extern "C" fn person_quote(ptr: *const Person, prefix_str: *const c_ushort,
 
 #[no_mangle]
 pub extern "C" fn person_quote_bytes(ptr: *const Person, prefix_str: *const c_char, prefix_len: c_int, suffix_str: *const c_char, suffix_len: c_int, d: *mut QString, set: fn(*mut QString, str: *const c_char, len: c_int)) {
-    let prefix = unsafe { slice::from_raw_parts(prefix_str as *const u8, prefix_len as usize) };
-    let suffix = unsafe { slice::from_raw_parts(suffix_str as *const u8, suffix_len as usize) };
+    let prefix = unsafe { slice::from_raw_parts(prefix_str as *const u8, to_usize(prefix_len)) };
+    let suffix = unsafe { slice::from_raw_parts(suffix_str as *const u8, to_usize(suffix_len)) };
     let o = unsafe { &*ptr };
     let r = o.quote_bytes(prefix, suffix);
     let s: *const c_char = r.as_ptr() as (*const c_char);
diff --git a/tests/rust_list/src/interface.rs b/tests/rust_list/src/interface.rs
index ba7e7a2..cd2adff 100644
--- a/tests/rust_list/src/interface.rs
+++ b/tests/rust_list/src/interface.rs
@@ -40,7 +40,7 @@ where
 pub enum QString {}
 
 fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
-    let utf16 = unsafe { slice::from_raw_parts(str, len as usize) };
+    let utf16 = unsafe { slice::from_raw_parts(str, to_usize(len)) };
     let characters = decode_utf16(utf16.iter().cloned())
         .into_iter()
         .map(|r| r.unwrap());
@@ -62,6 +62,23 @@ pub struct QModelIndex {
     internal_id: usize,
 }
 
+
+fn to_usize(n: c_int) -> usize {
+    if n < 0 {
+        panic!("Cannot cast {} to usize", n);
+    }
+    n as usize
+}
+
+
+fn to_c_int(n: usize) -> c_int {
+    if n > c_int::max_value() as usize {
+        panic!("Cannot cast {} to c_int", n);
+    }
+    n as c_int
+}
+
+
 pub struct PersonsQObject {}
 
 #[derive(Clone)]
@@ -171,15 +188,15 @@ pub unsafe extern "C" fn persons_free(ptr: *mut Persons) {
 
 #[no_mangle]
 pub unsafe extern "C" fn persons_row_count(ptr: *const Persons) -> c_int {
-    (&*ptr).row_count() as c_int
+    to_c_int((&*ptr).row_count())
 }
 #[no_mangle]
 pub unsafe extern "C" fn persons_insert_rows(ptr: *mut Persons, row: c_int, count: c_int) -> bool {
-    (&mut *ptr).insert_rows(row as usize, count as usize)
+    (&mut *ptr).insert_rows(to_usize(row), to_usize(count))
 }
 #[no_mangle]
 pub unsafe extern "C" fn persons_remove_rows(ptr: *mut Persons, row: c_int, count: c_int) -> bool {
-    (&mut *ptr).remove_rows(row as usize, count as usize)
+    (&mut *ptr).remove_rows(to_usize(row), to_usize(count))
 }
 #[no_mangle]
 pub unsafe extern "C" fn persons_can_fetch_more(ptr: *const Persons) -> bool {
@@ -205,9 +222,9 @@ pub extern "C" fn persons_data_user_name(
     set: fn(*mut QString, *const c_char, len: c_int),
 ) {
     let o = unsafe { &*ptr };
-    let data = o.user_name(row as usize);
+    let data = o.user_name(to_usize(row));
     let s: *const c_char = data.as_ptr() as (*const c_char);
-    set(d, s, data.len() as c_int);
+    set(d, s, to_c_int(data.len()));
 }
 
 #[no_mangle]
@@ -218,5 +235,5 @@ pub extern "C" fn persons_set_data_user_name(
     let o = unsafe { &mut *ptr };
     let mut v = String::new();
     set_string_from_utf16(&mut v, s, len);
-    o.set_user_name(row as usize, v)
+    o.set_user_name(to_usize(row), v)
 }
diff --git a/tests/rust_list_types/src/interface.rs b/tests/rust_list_types/src/interface.rs
index d2606fe..be4f34b 100644
--- a/tests/rust_list_types/src/interface.rs
+++ b/tests/rust_list_types/src/interface.rs
@@ -40,7 +40,7 @@ where
 pub enum QString {}
 
 fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
-    let utf16 = unsafe { slice::from_raw_parts(str, len as usize) };
+    let utf16 = unsafe { slice::from_raw_parts(str, to_usize(len)) };
     let characters = decode_utf16(utf16.iter().cloned())
         .into_iter()
         .map(|r| r.unwrap());
@@ -65,6 +65,23 @@ pub struct QModelIndex {
     internal_id: usize,
 }
 
+
+fn to_usize(n: c_int) -> usize {
+    if n < 0 {
+        panic!("Cannot cast {} to usize", n);
+    }
+    n as usize
+}
+
+
+fn to_c_int(n: usize) -> c_int {
+    if n > c_int::max_value() as usize {
+        panic!("Cannot cast {} to c_int", n);
+    }
+    n as c_int
+}
+
+
 pub struct ListQObject {}
 
 #[derive(Clone)]
@@ -204,15 +221,15 @@ pub unsafe extern "C" fn list_free(ptr: *mut List) {
 
 #[no_mangle]
 pub unsafe extern "C" fn list_row_count(ptr: *const List) -> c_int {
-    (&*ptr).row_count() as c_int
+    to_c_int((&*ptr).row_count())
 }
 #[no_mangle]
 pub unsafe extern "C" fn list_insert_rows(ptr: *mut List, row: c_int, count: c_int) -> bool {
-    (&mut *ptr).insert_rows(row as usize, count as usize)
+    (&mut *ptr).insert_rows(to_usize(row), to_usize(count))
 }
 #[no_mangle]
 pub unsafe extern "C" fn list_remove_rows(ptr: *mut List, row: c_int, count: c_int) -> bool {
-    (&mut *ptr).remove_rows(row as usize, count as usize)
+    (&mut *ptr).remove_rows(to_usize(row), to_usize(count))
 }
 #[no_mangle]
 pub unsafe extern "C" fn list_can_fetch_more(ptr: *const List) -> bool {
@@ -234,7 +251,7 @@ pub unsafe extern "C" fn list_sort(
 #[no_mangle]
 pub extern "C" fn list_data_boolean(ptr: *const List, row: c_int) -> bool {
     let o = unsafe { &*ptr };
-    o.boolean(row as usize).into()
+    o.boolean(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -242,7 +259,7 @@ pub unsafe extern "C" fn list_set_data_boolean(
     ptr: *mut List, row: c_int,
     v: bool,
 ) -> bool {
-    (&mut *ptr).set_boolean(row as usize, v)
+    (&mut *ptr).set_boolean(to_usize(row), v)
 }
 
 #[no_mangle]
@@ -252,9 +269,9 @@ pub extern "C" fn list_data_bytearray(
     set: fn(*mut QByteArray, *const c_char, len: c_int),
 ) {
     let o = unsafe { &*ptr };
-    let data = o.bytearray(row as usize);
+    let data = o.bytearray(to_usize(row));
     let s: *const c_char = data.as_ptr() as (*const c_char);
-    set(d, s, data.len() as c_int);
+    set(d, s, to_c_int(data.len()));
 }
 
 #[no_mangle]
@@ -263,14 +280,14 @@ pub extern "C" fn list_set_data_bytearray(
     s: *const c_char, len: c_int,
 ) -> bool {
     let o = unsafe { &mut *ptr };
-    let slice = unsafe { ::std::slice::from_raw_parts(s as *const u8, len as usize) };
-    o.set_bytearray(row as usize, slice)
+    let slice = unsafe { ::std::slice::from_raw_parts(s as *const u8, to_usize(len)) };
+    o.set_bytearray(to_usize(row), slice)
 }
 
 #[no_mangle]
 pub extern "C" fn list_data_f32(ptr: *const List, row: c_int) -> f32 {
     let o = unsafe { &*ptr };
-    o.f32(row as usize).into()
+    o.f32(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -278,13 +295,13 @@ pub unsafe extern "C" fn list_set_data_f32(
     ptr: *mut List, row: c_int,
     v: f32,
 ) -> bool {
-    (&mut *ptr).set_f32(row as usize, v)
+    (&mut *ptr).set_f32(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn list_data_f64(ptr: *const List, row: c_int) -> f64 {
     let o = unsafe { &*ptr };
-    o.f64(row as usize).into()
+    o.f64(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -292,13 +309,13 @@ pub unsafe extern "C" fn list_set_data_f64(
     ptr: *mut List, row: c_int,
     v: f64,
 ) -> bool {
-    (&mut *ptr).set_f64(row as usize, v)
+    (&mut *ptr).set_f64(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn list_data_i16(ptr: *const List, row: c_int) -> i16 {
     let o = unsafe { &*ptr };
-    o.i16(row as usize).into()
+    o.i16(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -306,13 +323,13 @@ pub unsafe extern "C" fn list_set_data_i16(
     ptr: *mut List, row: c_int,
     v: i16,
 ) -> bool {
-    (&mut *ptr).set_i16(row as usize, v)
+    (&mut *ptr).set_i16(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn list_data_i32(ptr: *const List, row: c_int) -> i32 {
     let o = unsafe { &*ptr };
-    o.i32(row as usize).into()
+    o.i32(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -320,13 +337,13 @@ pub unsafe extern "C" fn list_set_data_i32(
     ptr: *mut List, row: c_int,
     v: i32,
 ) -> bool {
-    (&mut *ptr).set_i32(row as usize, v)
+    (&mut *ptr).set_i32(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn list_data_i64(ptr: *const List, row: c_int) -> i64 {
     let o = unsafe { &*ptr };
-    o.i64(row as usize).into()
+    o.i64(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -334,13 +351,13 @@ pub unsafe extern "C" fn list_set_data_i64(
     ptr: *mut List, row: c_int,
     v: i64,
 ) -> bool {
-    (&mut *ptr).set_i64(row as usize, v)
+    (&mut *ptr).set_i64(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn list_data_i8(ptr: *const List, row: c_int) -> i8 {
     let o = unsafe { &*ptr };
-    o.i8(row as usize).into()
+    o.i8(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -348,13 +365,13 @@ pub unsafe extern "C" fn list_set_data_i8(
     ptr: *mut List, row: c_int,
     v: i8,
 ) -> bool {
-    (&mut *ptr).set_i8(row as usize, v)
+    (&mut *ptr).set_i8(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn list_data_optional_boolean(ptr: *const List, row: c_int) -> COption<bool> {
     let o = unsafe { &*ptr };
-    o.optional_boolean(row as usize).into()
+    o.optional_boolean(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -362,12 +379,12 @@ pub unsafe extern "C" fn list_set_data_optional_boolean(
     ptr: *mut List, row: c_int,
     v: bool,
 ) -> bool {
-    (&mut *ptr).set_optional_boolean(row as usize, Some(v))
+    (&mut *ptr).set_optional_boolean(to_usize(row), Some(v))
 }
 
 #[no_mangle]
 pub unsafe extern "C" fn list_set_data_optional_boolean_none(ptr: *mut List, row: c_int) -> bool {
-    (&mut *ptr).set_optional_boolean(row as usize, None)
+    (&mut *ptr).set_optional_boolean(to_usize(row), None)
 }
 
 #[no_mangle]
@@ -377,10 +394,10 @@ pub extern "C" fn list_data_optional_bytearray(
     set: fn(*mut QByteArray, *const c_char, len: c_int),
 ) {
     let o = unsafe { &*ptr };
-    let data = o.optional_bytearray(row as usize);
+    let data = o.optional_bytearray(to_usize(row));
     if let Some(data) = data {
         let s: *const c_char = data.as_ptr() as (*const c_char);
-        set(d, s, data.len() as c_int);
+        set(d, s, to_c_int(data.len()));
     }
 }
 
@@ -390,13 +407,13 @@ pub extern "C" fn list_set_data_optional_bytearray(
     s: *const c_char, len: c_int,
 ) -> bool {
     let o = unsafe { &mut *ptr };
-    let slice = unsafe { ::std::slice::from_raw_parts(s as *const u8, len as usize) };
-    o.set_optional_bytearray(row as usize, Some(slice))
+    let slice = unsafe { ::std::slice::from_raw_parts(s as *const u8, to_usize(len)) };
+    o.set_optional_bytearray(to_usize(row), Some(slice))
 }
 
 #[no_mangle]
 pub unsafe extern "C" fn list_set_data_optional_bytearray_none(ptr: *mut List, row: c_int) -> bool {
-    (&mut *ptr).set_optional_bytearray(row as usize, None)
+    (&mut *ptr).set_optional_bytearray(to_usize(row), None)
 }
 
 #[no_mangle]
@@ -406,10 +423,10 @@ pub extern "C" fn list_data_optional_string(
     set: fn(*mut QString, *const c_char, len: c_int),
 ) {
     let o = unsafe { &*ptr };
-    let data = o.optional_string(row as usize);
+    let data = o.optional_string(to_usize(row));
     if let Some(data) = data {
         let s: *const c_char = data.as_ptr() as (*const c_char);
-        set(d, s, data.len() as c_int);
+        set(d, s, to_c_int(data.len()));
     }
 }
 
@@ -421,12 +438,12 @@ pub extern "C" fn list_set_data_optional_string(
     let o = unsafe { &mut *ptr };
     let mut v = String::new();
     set_string_from_utf16(&mut v, s, len);
-    o.set_optional_string(row as usize, Some(v))
+    o.set_optional_string(to_usize(row), Some(v))
 }
 
 #[no_mangle]
 pub unsafe extern "C" fn list_set_data_optional_string_none(ptr: *mut List, row: c_int) -> bool {
-    (&mut *ptr).set_optional_string(row as usize, None)
+    (&mut *ptr).set_optional_string(to_usize(row), None)
 }
 
 #[no_mangle]
@@ -436,9 +453,9 @@ pub extern "C" fn list_data_string(
     set: fn(*mut QString, *const c_char, len: c_int),
 ) {
     let o = unsafe { &*ptr };
-    let data = o.string(row as usize);
+    let data = o.string(to_usize(row));
     let s: *const c_char = data.as_ptr() as (*const c_char);
-    set(d, s, data.len() as c_int);
+    set(d, s, to_c_int(data.len()));
 }
 
 #[no_mangle]
@@ -449,13 +466,13 @@ pub extern "C" fn list_set_data_string(
     let o = unsafe { &mut *ptr };
     let mut v = String::new();
     set_string_from_utf16(&mut v, s, len);
-    o.set_string(row as usize, v)
+    o.set_string(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn list_data_u16(ptr: *const List, row: c_int) -> u16 {
     let o = unsafe { &*ptr };
-    o.u16(row as usize).into()
+    o.u16(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -463,13 +480,13 @@ pub unsafe extern "C" fn list_set_data_u16(
     ptr: *mut List, row: c_int,
     v: u16,
 ) -> bool {
-    (&mut *ptr).set_u16(row as usize, v)
+    (&mut *ptr).set_u16(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn list_data_u32(ptr: *const List, row: c_int) -> u32 {
     let o = unsafe { &*ptr };
-    o.u32(row as usize).into()
+    o.u32(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -477,13 +494,13 @@ pub unsafe extern "C" fn list_set_data_u32(
     ptr: *mut List, row: c_int,
     v: u32,
 ) -> bool {
-    (&mut *ptr).set_u32(row as usize, v)
+    (&mut *ptr).set_u32(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn list_data_u64(ptr: *const List, row: c_int) -> u64 {
     let o = unsafe { &*ptr };
-    o.u64(row as usize).into()
+    o.u64(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -491,13 +508,13 @@ pub unsafe extern "C" fn list_set_data_u64(
     ptr: *mut List, row: c_int,
     v: u64,
 ) -> bool {
-    (&mut *ptr).set_u64(row as usize, v)
+    (&mut *ptr).set_u64(to_usize(row), v)
 }
 
 #[no_mangle]
 pub extern "C" fn list_data_u8(ptr: *const List, row: c_int) -> u8 {
     let o = unsafe { &*ptr };
-    o.u8(row as usize).into()
+    o.u8(to_usize(row)).into()
 }
 
 #[no_mangle]
@@ -505,5 +522,5 @@ pub unsafe extern "C" fn list_set_data_u8(
     ptr: *mut List, row: c_int,
     v: u8,
 ) -> bool {
-    (&mut *ptr).set_u8(row as usize, v)
+    (&mut *ptr).set_u8(to_usize(row), v)
 }
diff --git a/tests/rust_object/src/interface.rs b/tests/rust_object/src/interface.rs
index a23660f..0dc2d3a 100644
--- a/tests/rust_object/src/interface.rs
+++ b/tests/rust_object/src/interface.rs
@@ -14,7 +14,7 @@ use implementation::*;
 pub enum QString {}
 
 fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
-    let utf16 = unsafe { slice::from_raw_parts(str, len as usize) };
+    let utf16 = unsafe { slice::from_raw_parts(str, to_usize(len)) };
     let characters = decode_utf16(utf16.iter().cloned())
         .into_iter()
         .map(|r| r.unwrap());
@@ -23,6 +23,23 @@ fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
 }
 
 
+
+fn to_usize(n: c_int) -> usize {
+    if n < 0 {
+        panic!("Cannot cast {} to usize", n);
+    }
+    n as usize
+}
+
+
+fn to_c_int(n: usize) -> c_int {
+    if n > c_int::max_value() as usize {
+        panic!("Cannot cast {} to c_int", n);
+    }
+    n as c_int
+}
+
+
 pub struct PersonQObject {}
 
 #[derive(Clone)]
@@ -79,7 +96,7 @@ pub extern "C" fn person_user_name_get(
     let o = unsafe { &*ptr };
     let v = o.user_name();
     let s: *const c_char = v.as_ptr() as (*const c_char);
-    set(p, s, v.len() as c_int);
+    set(p, s, to_c_int(v.len()));
 }
 
 #[no_mangle]
diff --git a/tests/rust_object_types/src/interface.rs b/tests/rust_object_types/src/interface.rs
index e14d231..cf3e522 100644
--- a/tests/rust_object_types/src/interface.rs
+++ b/tests/rust_object_types/src/interface.rs
@@ -40,7 +40,7 @@ where
 pub enum QString {}
 
 fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
-    let utf16 = unsafe { slice::from_raw_parts(str, len as usize) };
+    let utf16 = unsafe { slice::from_raw_parts(str, to_usize(len)) };
     let characters = decode_utf16(utf16.iter().cloned())
         .into_iter()
         .map(|r| r.unwrap());
@@ -52,6 +52,23 @@ fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
 
 pub enum QByteArray {}
 
+
+fn to_usize(n: c_int) -> usize {
+    if n < 0 {
+        panic!("Cannot cast {} to usize", n);
+    }
+    n as usize
+}
+
+
+fn to_c_int(n: usize) -> c_int {
+    if n > c_int::max_value() as usize {
+        panic!("Cannot cast {} to c_int", n);
+    }
+    n as c_int
+}
+
+
 pub struct ObjectQObject {}
 
 #[derive(Clone)]
@@ -294,13 +311,13 @@ pub extern "C" fn object_bytearray_get(
     let o = unsafe { &*ptr };
     let v = o.bytearray();
     let s: *const c_char = v.as_ptr() as (*const c_char);
-    set(p, s, v.len() as c_int);
+    set(p, s, to_c_int(v.len()));
 }
 
 #[no_mangle]
 pub extern "C" fn object_bytearray_set(ptr: *mut Object, v: *const c_char, len: c_int) {
     let o = unsafe { &mut *ptr };
-    let v = unsafe { slice::from_raw_parts(v as *const u8, len as usize) };
+    let v = unsafe { slice::from_raw_parts(v as *const u8, to_usize(len)) };
     o.set_bytearray(v);
 }
 
@@ -393,14 +410,14 @@ pub extern "C" fn object_optional_bytearray_get(
     let v = o.optional_bytearray();
     if let Some(v) = v {
         let s: *const c_char = v.as_ptr() as (*const c_char);
-        set(p, s, v.len() as c_int);
+        set(p, s, to_c_int(v.len()));
     }
 }
 
 #[no_mangle]
 pub extern "C" fn object_optional_bytearray_set(ptr: *mut Object, v: *const c_char, len: c_int) {
     let o = unsafe { &mut *ptr };
-    let v = unsafe { slice::from_raw_parts(v as *const u8, len as usize) };
+    let v = unsafe { slice::from_raw_parts(v as *const u8, to_usize(len)) };
     o.set_optional_bytearray(Some(v.into()));
 }
 
@@ -420,7 +437,7 @@ pub extern "C" fn object_optional_string_get(
     let v = o.optional_string();
     if let Some(v) = v {
         let s: *const c_char = v.as_ptr() as (*const c_char);
-        set(p, s, v.len() as c_int);
+        set(p, s, to_c_int(v.len()));
     }
 }
 
@@ -466,7 +483,7 @@ pub extern "C" fn object_string_get(
     let o = unsafe { &*ptr };
     let v = o.string();
     let s: *const c_char = v.as_ptr() as (*const c_char);
-    set(p, s, v.len() as c_int);
+    set(p, s, to_c_int(v.len()));
 }
 
 #[no_mangle]
diff --git a/tests/rust_objects/src/interface.rs b/tests/rust_objects/src/interface.rs
index 7c39126..371ca53 100644
--- a/tests/rust_objects/src/interface.rs
+++ b/tests/rust_objects/src/interface.rs
@@ -14,7 +14,7 @@ use implementation::*;
 pub enum QString {}
 
 fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
-    let utf16 = unsafe { slice::from_raw_parts(str, len as usize) };
+    let utf16 = unsafe { slice::from_raw_parts(str, to_usize(len)) };
     let characters = decode_utf16(utf16.iter().cloned())
         .into_iter()
         .map(|r| r.unwrap());
@@ -23,6 +23,23 @@ fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
 }
 
 
+
+fn to_usize(n: c_int) -> usize {
+    if n < 0 {
+        panic!("Cannot cast {} to usize", n);
+    }
+    n as usize
+}
+
+
+fn to_c_int(n: usize) -> c_int {
+    if n > c_int::max_value() as usize {
+        panic!("Cannot cast {} to c_int", n);
+    }
+    n as c_int
+}
+
+
 pub struct GroupQObject {}
 
 #[derive(Clone)]
@@ -137,7 +154,7 @@ pub extern "C" fn inner_object_description_get(
     let o = unsafe { &*ptr };
     let v = o.description();
     let s: *const c_char = v.as_ptr() as (*const c_char);
-    set(p, s, v.len() as c_int);
+    set(p, s, to_c_int(v.len()));
 }
 
 #[no_mangle]
diff --git a/tests/rust_tree/src/interface.rs b/tests/rust_tree/src/interface.rs
index 594f00a..afa7b8e 100644
--- a/tests/rust_tree/src/interface.rs
+++ b/tests/rust_tree/src/interface.rs
@@ -40,7 +40,7 @@ where
 pub enum QString {}
 
 fn set_string_from_utf16(s: &mut String, str: *const c_ushort, len: c_int) {
-    let utf16 = unsafe { slice::from_raw_parts(str, len as usize) };
+    let utf16 = unsafe { slice::from_raw_parts(str, to_usize(len)) };
     let characters = decode_utf16(utf16.iter().cloned())
         .into_iter()
         .map(|r| r.unwrap());
@@ -62,6 +62,23 @@ pub struct QModelIndex {
     internal_id: usize,
 }
 
+
+fn to_usize(n: c_int) -> usize {
+    if n < 0 {
+        panic!("Cannot cast {} to usize", n);
+    }
+    n as usize
+}
+
+
+fn to_c_int(n: usize) -> c_int {
+    if n > c_int::max_value() as usize {
+        panic!("Cannot cast {} to c_int", n);
+    }
+    n as c_int
+}
+
+
 pub struct PersonsQObject {}
 
 #[derive(Clone)]
@@ -176,11 +193,11 @@ pub unsafe extern "C" fn persons_row_count(
     item: usize,
     valid: bool,
 ) -> c_int {
-    if valid {
-        (&*ptr).row_count(Some(item)) as c_int
+    to_c_int(if valid {
+        (&*ptr).row_count(Some(item))
     } else {
-        (&*ptr).row_count(None) as c_int
-    }
+        (&*ptr).row_count(None)
+    })
 }
 #[no_mangle]
 pub unsafe extern "C" fn persons_can_fetch_more(
@@ -218,16 +235,16 @@ pub unsafe extern "C" fn persons_index(
     row: c_int,
 ) -> usize {
     if !valid {
-        (&*ptr).index(None, row as usize)
+        (&*ptr).index(None, to_usize(row))
     } else {
-        (&*ptr).index(Some(item), row as usize)
+        (&*ptr).index(Some(item), to_usize(row))
     }
 }
 #[no_mangle]
 pub unsafe extern "C" fn persons_parent(ptr: *const Persons, index: usize) -> QModelIndex {
     if let Some(parent) = (&*ptr).parent(index) {
         QModelIndex {
-            row: (&*ptr).row(parent) as c_int,
+            row: to_c_int((&*ptr).row(parent)),
             internal_id: parent,
         }
     } else {
@@ -239,7 +256,7 @@ pub unsafe extern "C" fn persons_parent(ptr: *const Persons, index: usize) -> QM
 }
 #[no_mangle]
 pub unsafe extern "C" fn persons_row(ptr: *const Persons, item: usize) -> c_int {
-    (&*ptr).row(item) as c_int
+    to_c_int((&*ptr).row(item))
 }
 
 #[no_mangle]
@@ -251,7 +268,7 @@ pub extern "C" fn persons_data_user_name(
     let o = unsafe { &*ptr };
     let data = o.user_name(item);
     let s: *const c_char = data.as_ptr() as (*const c_char);
-    set(d, s, data.len() as c_int);
+    set(d, s, to_c_int(data.len()));
 }
 
 #[no_mangle]