diff --git a/GPy/testing/mapping_tests.py b/GPy/testing/mapping_tests.py
index 24eefb92..23013f92 100644
--- a/GPy/testing/mapping_tests.py
+++ b/GPy/testing/mapping_tests.py
@@ -46,7 +46,7 @@ class MappingTests(unittest.TestCase):
 
     def test_mlpextmapping(self):
         for activation in ['tanh', 'relu', 'sigmoid']:
-            mapping = GPy.mappings.MLPext(input_dim=3, hidden_dims=[5,5,5], output_dim=2, activation=activation)
+            mapping = GPy.mappings.MLPext(input_dim=3, hidden_dims=[5,5], output_dim=2, activation=activation)
             X = np.random.randn(100,3)
             self.assertTrue(MappingGradChecker(mapping, X).checkgrad())