diff --git a/GPy/kern/__init__.py b/GPy/kern/__init__.py
index e5dc6d35..594ff6d3 100644
--- a/GPy/kern/__init__.py
+++ b/GPy/kern/__init__.py
@@ -2,9 +2,9 @@ from _src.rbf import RBF
 from _src.white import White
 from _src.kern import Kern
 from _src.linear import Linear
+from _src.bias import Bias
 from _src.brownian import Brownian
 from _src.stationary import Exponential, Matern32, Matern52, ExpQuad
-#from _src.bias import Bias
 #import coregionalize
 #import exponential
 #import eq_ode1
diff --git a/GPy/kern/_src/bias.py b/GPy/kern/_src/bias.py
index d45561f8..e1938c95 100644
--- a/GPy/kern/_src/bias.py
+++ b/GPy/kern/_src/bias.py
@@ -5,6 +5,7 @@
 from kern import Kern
 from ...core.parameterization import Param
 from ...core.parameterization.transformations import Logexp
+import numpy as np
 
 class Bias(Kern):
     def __init__(self,input_dim,variance=1.,name=None):
diff --git a/GPy/kern/_src/stationary.py b/GPy/kern/_src/stationary.py
index 7cc2e695..a6ff9424 100644
--- a/GPy/kern/_src/stationary.py
+++ b/GPy/kern/_src/stationary.py
@@ -18,7 +18,7 @@ class Stationary(Kern):
                 lengthscale = np.ones(1)
             else:
                 lengthscale = np.asarray(lengthscale)
-                assert lengthscale.size == 1 "Only  lengthscale needed for non-ARD kernel"
+                assert lengthscale.size == 1, "Only  lengthscale needed for non-ARD kernel"
         else:
             if lengthscale is not None:
                 lengthscale = np.asarray(lengthscale)