diff --git a/lib/js.defs b/lib/js.defs
index 9508c3083e..570ed1ec47 100644
--- a/lib/js.defs
+++ b/lib/js.defs
@@ -165,5 +165,5 @@ def vulcanize(
       '--js', '%s.js' % name,
       '&&', 'zip', '$OUT', '%s.html' % name, '%s.js' % name,
     ]),
-    out = '%s.vulcanized.zip',
+    out = '%s.vulcanized.zip' % name,
   )