diff --git a/mode/diff.py b/mode/diff.py
index e9a4614..4b96c6f 100644
--- a/mode/diff.py
+++ b/mode/diff.py
@@ -13,7 +13,7 @@ class DiffGrammar(Grammar):
 
 class Diff(Fundamental):
     name       = 'diff'
-    extensions = ['.patch', '.diff']
+    extensions = ['.patch', '.diff', '.rej']
     grammar    = DiffGrammar()
     colors     = {
         'diff.left':      ('red', 'default', 'bold'),