diff --git a/boltons/typeutils.py b/boltons/typeutils.py
index 395ce590..875e2e2b 100644
--- a/boltons/typeutils.py
+++ b/boltons/typeutils.py
@@ -91,7 +91,7 @@ def __bool__(self):
         def __copy__(self):
             return self
 
-        def __deepcopy__(self):
+        def __deepcopy__(self, _memo):
             return self
 
     if var_name: