diff --git a/cacheflow/utils.py b/cacheflow/utils.py
index 485e18f6d..fff6b7a86 100644
--- a/cacheflow/utils.py
+++ b/cacheflow/utils.py
@@ -11,7 +11,7 @@ class Counter:
     def __init__(self, start: int = 0) -> None:
         self.counter = start
 
-    def next(self) -> int:
+    def __next__(self) -> int:
         id = self.counter
         self.counter += 1
         return id