diff --git a/Lib/pickle.py b/Lib/pickle.py
index 508e858..299de16 100644
--- a/Lib/pickle.py
+++ b/Lib/pickle.py
@@ -269,7 +269,7 @@
     def save(self, obj):
         # Check for persistent id (defined by a subclass)
         pid = self.persistent_id(obj)
-        if pid:
+        if pid is not None:
             self.save_pers(pid)
             return