diff --git a/source/bin.rs b/source/bin.rs
index 3c88b9a..e63b63a 100644
--- a/source/bin.rs
+++ b/source/bin.rs
@@ -160,6 +160,9 @@ macro_rules! rd_impl {
 /// ```
 /// # #[macro_use] extern crate maraiah;
 /// # use maraiah::err::*;
+/// #
+/// # fn main() -> ResultS<()>
+/// # {
 /// let buffer = &[4, 0, 2, 0, 0, 0, 6];
 ///
 /// read_data! {
@@ -176,6 +179,7 @@ macro_rules! rd_impl {
 /// assert_eq!(six, 6_u8);
 /// assert_eq!(byte, &[2, 0, 0, 0]);
 /// # Ok(())
+/// # }
 /// ```
 #[macro_export]
 macro_rules! read_data {
@@ -185,20 +189,24 @@ macro_rules! read_data {
            $($ex:ident$(::$exc:ident)*)*;)*
       }
    ) => {
-      $crate::check_data!($at + $sz, $b);
+      $crate::bin::check_data($b, $at + $sz)?;
       $($crate::rd_impl!($e, $b, $at, $n;
                          $($rn;)? $nam, $($ex$(::$exc)*,)* $t$(::$tc)*);)*
    };
 }
 
 /// Checks if there is enough data in `b`.
-#[macro_export]
-macro_rules! check_data {
-   ($sz:expr, $b:expr) => {
-      if $b.len() < $sz {
-         return Err(err_msg("not enough data"));
-      }
-   };
+///
+/// # Errors
+///
+/// Returns `Err` if `b.len()` is less than `sz`.
+pub fn check_data(b: &[u8], sz: usize) -> ResultS<()>
+{
+   if b.len() < sz {
+      Err(err_msg("not enough data"))
+   } else {
+      Ok(())
+   }
 }
 
 /// Casts a `u32` to a `usize`.
@@ -417,7 +425,7 @@ pub fn rd_ofstable<T, F>(b: &[u8],
 
    for _ in 0..num {
       let ofs = usize_from_u32(u32b(&b[p..p + 4]));
-      check_data!(ofs, b);
+      check_data(b, ofs)?;
       v.push(read(&b[ofs..])?);
       p += 4;
    }
diff --git a/source/defl.rs b/source/defl.rs
index 59a2af0..ad29d11 100644
--- a/source/defl.rs
+++ b/source/defl.rs
@@ -1,6 +1,6 @@
 //! DEFLATE loader.
 
-use crate::{bit::*, err::*};
+use crate::{bin::check_data, bit::*, err::*};
 use std::cmp::Ordering;
 
 /// Loads a ZLIB file header.
@@ -76,7 +76,7 @@ pub fn load_gzip_header(b: &[u8]) -> ResultS<usize>
 
       p += 2 + xlen;
 
-      check_data!(p, b);
+      check_data(b, p)?;
    }
 
    if fl & FNAME != 0 {
@@ -90,7 +90,7 @@ pub fn load_gzip_header(b: &[u8]) -> ResultS<usize>
    if fl & FHCRC != 0 {
       p += 2;
 
-      check_data!(p, b);
+      check_data(b, p)?;
    }
 
    Ok(p)
diff --git a/source/map/iidx.rs b/source/map/iidx.rs
index adc40c0..9dc4f4d 100644
--- a/source/map/iidx.rs
+++ b/source/map/iidx.rs
@@ -1,11 +1,11 @@
 //! `iidx` chunk.
 
-use crate::{bin::u16b, err::*};
+use crate::{bin::{check_data, u16b}, err::*};
 
 /// Reads an `iidx` chunk.
 pub fn read(b: &[u8]) -> ResultS<(u16, usize)>
 {
-   check_data!(2, b);
+   check_data(b, 2)?;
 
    Ok((u16b(b), 2))
 }