diff --git a/hw5/ooc.py b/hw5/ooc.py
index 11d5606..34d93f3 100644
--- a/hw5/ooc.py
+++ b/hw5/ooc.py
@@ -89,7 +89,7 @@ class MemoryLimitedHashMap(object):
     return key
 
   def path2Subkey(self, k):
-    key = k.split("_")
+    key = tuple(k.split("_"))
     return key
 
   def flushKey(self, k, subkey=""):