diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index 285acba138e..4c7b4bee398 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -416,6 +416,9 @@ def __sub__(self, other):
                 del data[x]
         return result
 
+    def __iter__(self):
+        return iter(self.data)
+
     def tolist(self, sorted=1):
         "Return _Set elements as a list."
         data = self.data.keys()