diff --git a/filterpy/common/helpers.py b/filterpy/common/helpers.py
index 0d54eed..6fb9291 100644
--- a/filterpy/common/helpers.py
+++ b/filterpy/common/helpers.py
@@ -88,14 +88,16 @@ def setter_scalar(value, dim_x):
     type which converts to numpy.array (list, np.array, np.matrix, etc),
     or a scalar, in which case we create a diagonal matrix with each
     diagonal element == value.
+
+    dim_x is used iff value is scalar, otherwise it is determined from the
+    shape of value
     """
     if isscalar(value):
         v = eye(dim_x) * value
     else:
-        v = asarray(value, dtype=float)
+        v = array(value, dtype=float)
+        dim_x = v.shape[0]
 
-    if v is value:
-        v = value.copy()
     if v.shape != (dim_x, dim_x):
         raise Exception('must have shape ({},{})'.format(dim_x, dim_x))
     return v