diff --git a/GPy/core/parameterization/parameter_core.py b/GPy/core/parameterization/parameter_core.py
index 55fe660c..94567761 100644
--- a/GPy/core/parameterization/parameter_core.py
+++ b/GPy/core/parameterization/parameter_core.py
@@ -424,7 +424,7 @@ class Parameterizable(Constrainable, Observable):
         
         return s
 
-    def _notify_parameters_changed(self, which):
+    def _notify_parameters_changed(self):
         self.parameters_changed()
         self._notify_observers()
         if self.has_parent():