diff --git a/source/marathon/defl.rs b/source/marathon/defl.rs
new file mode 100644
index 0000000..b07bd3b
--- /dev/null
+++ b/source/marathon/defl.rs
@@ -0,0 +1,62 @@
+//! DEFLATE loader.
+
+use crate::durandal::err::*;
+
+/// Loads a GZIP file header.
+pub fn load_gzip_header(b: &[u8]) -> ResultS<usize>
+{
+   const FHCRC:    u8 = 1 << 1;
+   const FEXTRA:   u8 = 1 << 2;
+   const FNAME:    u8 = 1 << 3;
+   const FCOMMENT: u8 = 1 << 4;
+
+   read_data! {
+      10, LE in b =>
+      id = u16[0];
+      cm =  u8[2];
+      fl =  u8[3];
+   }
+
+   if id != 0x8B1F || cm != 8 {
+      bail!("not gzip format");
+   }
+
+   let mut p = 10;
+
+   if fl & FEXTRA != 0 {
+      read_data!(p + 2, LE in b => xlen = u16[p] usize;);
+
+      if p + 2 + xlen > b.len() {
+         bail!("not enough data");
+      }
+
+      p += xlen;
+   }
+
+   if fl & FNAME != 0 {
+      p = skip_zero_terminated_item(&b[p..])?;
+   }
+
+   if fl & FCOMMENT != 0 {
+      p = skip_zero_terminated_item(&b[p..])?;
+   }
+
+   if fl & FHCRC != 0 {
+      read_data!(p + 2, LE in b => _crc = u16[p];);
+
+      p += 2;
+   }
+
+   Ok(p)
+}
+
+fn skip_zero_terminated_item(b: &[u8]) -> ResultS<usize>
+{
+   if let Some(i) = b.iter().position(|&n| n == 0) {
+      Ok(i)
+   } else {
+      bail!("no end of zero terminated item");
+   }
+}
+
+// EOF
diff --git a/source/marathon/mod.rs b/source/marathon/mod.rs
index 86fc790..f596331 100644
--- a/source/marathon/mod.rs
+++ b/source/marathon/mod.rs
@@ -1,5 +1,6 @@
 //! Library for file format data readers.
 
+pub mod defl;
 pub mod machdr;
 pub mod map;
 pub mod phy;
diff --git a/tests/data/gzipbad1.bin b/tests/data/gzipbad1.bin
new file mode 100644
index 0000000..d56535e
Binary files /dev/null and b/tests/data/gzipbad1.bin differ
diff --git a/tests/data/gzipbad2.bin b/tests/data/gzipbad2.bin
new file mode 100644
index 0000000..e4e84f5
Binary files /dev/null and b/tests/data/gzipbad2.bin differ
diff --git a/tests/data/gzipbad3.bin b/tests/data/gzipbad3.bin
new file mode 100644
index 0000000..c8a57dc
Binary files /dev/null and b/tests/data/gzipbad3.bin differ
diff --git a/tests/data/gzipbad4.bin b/tests/data/gzipbad4.bin
new file mode 100644
index 0000000..f5bebda
Binary files /dev/null and b/tests/data/gzipbad4.bin differ
diff --git a/tests/data/gzipbad5.bin b/tests/data/gzipbad5.bin
new file mode 100644
index 0000000..160dab7
Binary files /dev/null and b/tests/data/gzipbad5.bin differ
diff --git a/tests/data/gzipbad6.bin b/tests/data/gzipbad6.bin
new file mode 100644
index 0000000..8a4fa68
Binary files /dev/null and b/tests/data/gzipbad6.bin differ
diff --git a/tests/data/gzipbad7.bin b/tests/data/gzipbad7.bin
new file mode 100644
index 0000000..ed51912
Binary files /dev/null and b/tests/data/gzipbad7.bin differ
diff --git a/tests/data/gzipok1.bin b/tests/data/gzipok1.bin
new file mode 100644
index 0000000..be9e170
Binary files /dev/null and b/tests/data/gzipok1.bin differ
diff --git a/tests/data/gzipok2.bin b/tests/data/gzipok2.bin
new file mode 100644
index 0000000..cafa27c
Binary files /dev/null and b/tests/data/gzipok2.bin differ
diff --git a/tests/data/gzipok3.bin b/tests/data/gzipok3.bin
new file mode 100644
index 0000000..347a4aa
Binary files /dev/null and b/tests/data/gzipok3.bin differ
diff --git a/tests/defl.rs b/tests/defl.rs
new file mode 100644
index 0000000..58a503b
--- /dev/null
+++ b/tests/defl.rs
@@ -0,0 +1,29 @@
+use maraiah::marathon::defl::{self, load_gzip_header};
+
+include!("data/rand.rs");
+
+#[test]
+fn defl_must_succeed()
+{
+   assert!(load_gzip_header(include_bytes!("data/gzipok1.bin")).is_ok());
+   assert!(load_gzip_header(include_bytes!("data/gzipok2.bin")).is_ok());
+   assert!(load_gzip_header(include_bytes!("data/gzipok3.bin")).is_ok());
+}
+
+#[test]
+fn defl_must_not_succeed()
+{
+   for inp in &RANDOM {
+      assert!(defl::load_gzip_header(inp).is_err());
+   }
+
+   assert!(load_gzip_header(include_bytes!("data/gzipbad1.bin")).is_err());
+   assert!(load_gzip_header(include_bytes!("data/gzipbad2.bin")).is_err());
+   assert!(load_gzip_header(include_bytes!("data/gzipbad3.bin")).is_err());
+   assert!(load_gzip_header(include_bytes!("data/gzipbad4.bin")).is_err());
+   assert!(load_gzip_header(include_bytes!("data/gzipbad5.bin")).is_err());
+   assert!(load_gzip_header(include_bytes!("data/gzipbad6.bin")).is_err());
+   assert!(load_gzip_header(include_bytes!("data/gzipbad7.bin")).is_err());
+}
+
+// EOF