diff --git a/src/zennit/rules.py b/src/zennit/rules.py
index c918916..e2f9ff1 100644
--- a/src/zennit/rules.py
+++ b/src/zennit/rules.py
@@ -471,7 +471,7 @@ def copy(self):
     def max_fn(self, input, kernel_size, stride, padding, dilation):
         raise NotImplementedError("Implement in subclass")
 
-    def sum_fn(self, input, kernel, stride, padding, dilation):
+    def sum_fn(self, input, kernel_size, stride, padding, dilation):
         raise NotImplementedError("Implement in subclass")
 
     def forward(self, module, input, output):