diff --git a/GPy/kern/kern.py b/GPy/kern/kern.py
index 414a911f..ca9d80ea 100644
--- a/GPy/kern/kern.py
+++ b/GPy/kern/kern.py
@@ -70,8 +70,8 @@ class kern(parameterised):
                     ard_params = 1./p.lengthscale
 
                 ax.bar(np.arange(len(ard_params)) - 0.4, ard_params)
-                ax.set_xticks(np.arange(len(ard_params)),
-                              ["${}$".format(i + 1) for i in range(len(ard_params))])
+                ax.set_xticks(np.arange(len(ard_params)))
+                ax.set_xticklabels([r"${}$".format(i + 1) for i in range(len(ard_params))])
         return ax
 
     def _transform_gradients(self,g):