diff --git a/src/twisted/test/test_policies.py b/src/twisted/test/test_policies.py
index fdab1e1a6ab..33258e7c77c 100644
--- a/src/twisted/test/test_policies.py
+++ b/src/twisted/test/test_policies.py
@@ -357,7 +357,8 @@ def test_breakReferenceCycle(self):
 
 
 class WrappingFactory(policies.WrappingFactory):
-    protocol = lambda s, f, p: p
+    def protocol(self, f, p):
+        return p
 
     def startFactory(self):
         policies.WrappingFactory.startFactory(self)