diff --git a/.gitignore b/.gitignore
index b7831832c701..e9864e250433 100644
--- a/.gitignore
+++ b/.gitignore
@@ -98,6 +98,7 @@ TAGS
 /external/*/*.exe
 /external/*/*.manifest
 /external/*/*.txt
+/external/*/*.msm
 /moz/zipped/*.zip
 /extras/source/extensions