diff --git a/loopy/library/reduction.py b/loopy/library/reduction.py
index fa382cb451e7793d414157652f32360311c91397..865ed1d66fd060716743b0c8ee499c3b05f017cb 100644
--- a/loopy/library/reduction.py
+++ b/loopy/library/reduction.py
@@ -170,7 +170,7 @@ class ArgExtFunction(FunctionIdentifier):
         self.name = name
         self.inames = inames
 
-    def __getinitargs(self):
+    def __getinitargs__(self):
         return (self.reduction_op, self.scalar_dtype, self.name, self.inames)