diff --git a/Lib/difflib.py b/Lib/difflib.py
index 408079b..831840d 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1310,7 +1310,7 @@
 
 def _mdiff(fromlines, tolines, context=None, linejunk=None,
            charjunk=IS_CHARACTER_JUNK):
-    """Returns generator yielding marked up from/to side by side differences.
+    r"""Returns generator yielding marked up from/to side by side differences.
 
     Arguments:
     fromlines -- list of text lines to compared to tolines