diff --git a/GPy/testing/kernel_tests.py b/GPy/testing/kernel_tests.py
index a0fc5a3d..a78ef69a 100644
--- a/GPy/testing/kernel_tests.py
+++ b/GPy/testing/kernel_tests.py
@@ -636,7 +636,14 @@ class Coregionalize_cython_test(unittest.TestCase):
         grads_cython = self.k.gradient.copy()
 
         K_numpy = self.k._K_numpy(self.X)
+        # Nasty hack to ensure the numpy version is used for update_gradients
+        # If this test is running, cython is working, so override the cython
+        # function with the numpy function
+        _gradient_reduce_cython = self.k._gradient_reduce_cython
+        self.k._gradient_reduce_cython = self.k._gradient_reduce_numpy
         self.k.update_gradients_full(dL_dK, self.X)
+        # Undo hack
+        self.k._gradient_reduce_cython = _gradient_reduce_cython
         grads_numpy = self.k.gradient.copy()
 
         self.assertTrue(np.allclose(K_numpy, K_cython))
@@ -651,7 +658,12 @@ class Coregionalize_cython_test(unittest.TestCase):
 
         K_numpy = self.k._K_numpy(self.X, self.X2)
         self.k.gradient = 0.
+        # Same hack as in test_sym (Line 639)
+        _gradient_reduce_cython = self.k._gradient_reduce_cython
+        self.k._gradient_reduce_cython = self.k._gradient_reduce_numpy
         self.k.update_gradients_full(dL_dK, self.X, self.X2)
+        # Undo hack
+        self.k._gradient_reduce_cython = _gradient_reduce_cython
         grads_numpy = self.k.gradient.copy()
 
         self.assertTrue(np.allclose(K_numpy, K_cython))