diff --git a/lib/chibi/zlib.scm b/lib/chibi/zlib.scm
index 3baa0c7b..c2cf44e2 100644
--- a/lib/chibi/zlib.scm
+++ b/lib/chibi/zlib.scm
@@ -35,3 +35,13 @@
 
 (define (gunzip bvec)
   (process-pipe-bytevector '("gzip" "-c" "-d") bvec))
+
+;;> Gunzip decompress a bytevector in memory if it has been
+;;> compressed, or return as-is otherwise.
+
+(define (maybe-gunzip bvec)
+  (if (and (>= (bytevector-length bvec) 10)
+           (eqv? #x1f (bytevector-u8-ref bvec 0))
+           (eqv? #x8b (bytevector-u8-ref bvec 1)))
+      (gunzip bvec)
+      bvec))
diff --git a/lib/chibi/zlib.sld b/lib/chibi/zlib.sld
index 576b4515..252b46a0 100644
--- a/lib/chibi/zlib.sld
+++ b/lib/chibi/zlib.sld
@@ -1,5 +1,5 @@
 
 (define-library (chibi zlib)
-  (export gzip-file gunzip-file gzip gunzip)
+  (export gzip-file gunzip-file gzip gunzip maybe-gunzip)
   (import (scheme base) (chibi io) (chibi process))
   (include "zlib.scm"))