diff --git a/onnxscript/rewriter/_ir_utils.py b/onnxscript/rewriter/_ir_utils.py
index 9bee21642..cefbec823 100644
--- a/onnxscript/rewriter/_ir_utils.py
+++ b/onnxscript/rewriter/_ir_utils.py
@@ -89,7 +89,7 @@ def is_singleton_value(
     scalar = get_singleton_value(val)
     if scalar is None:
         return False
-    if isinstance(expected, Callable):
+    if callable(expected):
         return expected(scalar)
     if isinstance(expected, int):
         return expected == scalar