diff --git a/flake8/__init__.py b/flake8/__init__.py
index f3830b5..d9626cd 100644
--- a/flake8/__init__.py
+++ b/flake8/__init__.py
@@ -116,6 +116,8 @@ def hg_hook(ui, repo, **kwargs):
     files = []
     for rev in xrange(repo[kwargs['node']], len(repo)):
         for file_ in repo[rev].files():
+            if not file_.endswith('.py'):
+                continue
             if file_ not in files:
                 files.append(file_)