diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index 4aeda855..32dc5780 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -788,6 +788,8 @@ M:
   aliases:
   - mumps
   primary_extension: .mumps
+  extensions:
+  - .m
 
 Makefile:
   aliases: