diff --git a/pygit2/repository.py b/pygit2/repository.py
index 2605eee3..b5e59e87 100644
--- a/pygit2/repository.py
+++ b/pygit2/repository.py
@@ -614,7 +614,7 @@ def diff(
             If 'b' is None, by default the working directory is compared to 'a'.
             If 'cached' is set to True, the index/staging area is used for comparing.
 
-        flag
+        flags
             A combination of enums.DiffOption constants.
 
         context_lines