diff --git a/GPy/kern/_src/mlp.py b/GPy/kern/_src/mlp.py
index 4488ea82..e319b8b4 100644
--- a/GPy/kern/_src/mlp.py
+++ b/GPy/kern/_src/mlp.py
@@ -78,7 +78,7 @@ class MLP(Kern):
                            *((vec1[:, None]+vec2[None, :])*self.weight_variance
                              + 2*self.bias_variance + 2.))*base_cov_grad).sum()
 
-    def update_gradients_diag(self, X):
+    def update_gradients_diag(self, dL_dKdiag, X):
         self._K_diag_computations(X)
         self.variance.gradient = np.sum(self._K_diag_dvar*dL_dKdiag)