diff --git a/SimPEG/mesh/TensorMesh.py b/SimPEG/mesh/TensorMesh.py
index 30eebc13..4c0841b8 100644
--- a/SimPEG/mesh/TensorMesh.py
+++ b/SimPEG/mesh/TensorMesh.py
@@ -33,14 +33,16 @@ class TensorMesh(BaseMesh, TensorView, DiffOperators, InnerProducts):
     """
     _meshType = 'TENSOR'
 
-    def __init__(self, h, x0=None):
-        for i, h_i in enumerate(h):
+    def __init__(self, h_in, x0=None):
+        assert type(h_in) is list, 'h_in must be a list'
+        h = range(len(h_in))
+        for i, h_i in enumerate(h_in):
             if type(h_i) in [int, long, float]:
                 # This gives you something over the unit cube.
                 h_i = np.ones(int(h_i))/int(h_i)
-                h[i] = h_i
             assert type(h_i) == np.ndarray, ("h[%i] is not a numpy array." % i)
             assert len(h_i.shape) == 1, ("h[%i] must be a 1D numpy array." % i)
+            h[i] = h_i[:] # make a copy.
 
         BaseMesh.__init__(self, np.array([x.size for x in h]), x0)
         assert len(h) == len(self.x0), "Dimension mismatch. x0 != len(h)"