diff --git a/sphinx/ext/inheritance_diagram.py b/sphinx/ext/inheritance_diagram.py
index 7775305f5..05eb15895 100644
--- a/sphinx/ext/inheritance_diagram.py
+++ b/sphinx/ext/inheritance_diagram.py
@@ -186,7 +186,7 @@ class InheritanceGraph(object):
         for cls in classes:
             recurse(cls)
 
-        return all_classes.values()
+        return list(all_classes.values())
 
     def class_name(self, cls, parts=0):
         """Given a class object, return a fully-qualified name.