diff --git a/third_party/zip/README.cosmo b/third_party/zip/README.cosmo
index 69fbf8c30..309554994 100644
--- a/third_party/zip/README.cosmo
+++ b/third_party/zip/README.cosmo
@@ -11,4 +11,5 @@ ORIGIN
 LOCAL CHANGES
 
   - Use Cosmopolitan's PCLMUL optimized CRC32
+  - Don't magically append .zip extension to filename argument
   - Improve find_next_signature() performance using unlocked stdio
diff --git a/third_party/zip/zipfile.c b/third_party/zip/zipfile.c
index b03470d79..787e73ea4 100644
--- a/third_party/zip/zipfile.c
+++ b/third_party/zip/zipfile.c
@@ -413,6 +413,10 @@ char *ziptyp(s)
   if ((t = malloc(strlen(s) + 5)) == NULL)
     return NULL;
   strcpy(t, s);
+
+  // [jart] don't magically append .zip extension to filename argument
+  if (1) return t;
+
 #  ifdef __human68k__
   _toslash(t);
 #  endif