diff --git a/source/marathon/defl.rs b/source/marathon/defl.rs
index ddc8d8c..d2c3f68 100644
--- a/source/marathon/defl.rs
+++ b/source/marathon/defl.rs
@@ -2,6 +2,34 @@
 
 use crate::durandal::err::*;
 
+/// Loads a ZLIB file header.
+pub fn load_zlib_header(b: &[u8]) -> ResultS<usize>
+{
+   const CM:    u8 = 0b00001111;
+   const CINFO: u8 = 0b11110000;
+   const FDICT: u8 = 0b00100000;
+
+   read_data! {
+      2, BE in b =>
+      fcheck = u16[0];
+      cmf    =  u8[0];
+      flg    =  u8[1];
+   }
+
+   let cm    = cmf & CM;
+   let cinfo = cmf & CINFO >> 4;
+
+   if cm != 8 || fcheck % 31 != 0 || cinfo > 7 {
+      bail!("not zlib format");
+   }
+
+   if flg & FDICT != 0 {
+      bail!("dictionary not supported");
+   }
+
+   Ok(2)
+}
+
 /// Loads a GZIP file header.
 pub fn load_gzip_header(b: &[u8]) -> ResultS<usize>
 {