diff --git a/python/mozbuild/mozpack/chrome/manifest.py b/python/mozbuild/mozpack/chrome/manifest.py
index a578ff5bd2a0..e110a65a100e 100644
--- a/python/mozbuild/mozpack/chrome/manifest.py
+++ b/python/mozbuild/mozpack/chrome/manifest.py
@@ -364,4 +364,5 @@ def is_manifest(path):
     Return whether the given path is that of a manifest file.
     '''
     return path.endswith('.manifest') and not path.endswith('.CRT.manifest') \
-        and not path.endswith('.exe.manifest')
+        and not path.endswith('.exe.manifest') \
+        and os.path.basename(path) != "cose.manifest"