diff --git a/django/contrib/gis/measure.py b/django/contrib/gis/measure.py
index 1feb63f081..75ab53474c 100644
--- a/django/contrib/gis/measure.py
+++ b/django/contrib/gis/measure.py
@@ -1,14 +1,40 @@
+# Copyright (c) 2007, Robert Coup <robert.coup@onetrackmind.co.nz>
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification,
+# are permitted provided that the following conditions are met:
+#
+#   1. Redistributions of source code must retain the above copyright notice,
+#      this list of conditions and the following disclaimer.
+#
+#   2. Redistributions in binary form must reproduce the above copyright
+#      notice, this list of conditions and the following disclaimer in the
+#      documentation and/or other materials provided with the distribution.
+#
+#   3. Neither the name of Distance nor the names of its contributors may be used
+#      to endorse or promote products derived from this software without
+#      specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
 """
 Distance and Area objects to allow for sensible and convienient calculation 
 and conversions.
 
+Author: Robert Coup
+
 Inspired by GeoPy (http://exogen.case.edu/projects/geopy/)
 and Geoff Biggs' PhD work on dimensioned units for robotics.
-
-Copyright (c) 2007, Robert Coup <robert.coup@onetrackmind.co.nz>
 """
-
-from math import *
 from decimal import Decimal
 
 class Distance(object):
@@ -32,7 +58,7 @@ class Distance(object):
             else:
                 raise AttributeError("Unknown unit type: " + unit)
 
-        if default_unit:
+        if default_unit and isinstance(default_unit, str):
             self._default_unit = default_unit
     
     def __getattr__(self, name):