diff --git a/django/contrib/gis/db/backend/postgis/query.py b/django/contrib/gis/db/backend/postgis/query.py
index 1b8c3fa029..2610173673 100644
--- a/django/contrib/gis/db/backend/postgis/query.py
+++ b/django/contrib/gis/db/backend/postgis/query.py
@@ -228,7 +228,7 @@ def get_geo_where_clause(lookup_type, table_prefix, field, value):
             if lookup_type == 'relate': 
                 op = op(value[1])
             elif lookup_type in DISTANCE_FUNCTIONS and lookup_type != 'dwithin':
-                if field._unit_name == 'degree':
+                if field.geodetic:
                     # Geodetic distances are only availble from Points to PointFields.
                     if field._geom != 'POINT':
                         raise TypeError('PostGIS spherical operations are only valid on PointFields.')
diff --git a/django/contrib/gis/db/models/fields/__init__.py b/django/contrib/gis/db/models/fields/__init__.py
index 8948854b35..264ba40509 100644
--- a/django/contrib/gis/db/models/fields/__init__.py
+++ b/django/contrib/gis/db/models/fields/__init__.py
@@ -79,15 +79,22 @@ class GeometryField(SpatialBackend.Field):
         super(GeometryField, self).__init__(**kwargs) # Calling the parent initializtion function
 
     ### Routines specific to GeometryField ###
-    def get_distance(self, dist):
+    @property
+    def geodetic(self):
+        return self._unit_name in self.geodetic_units
+
+    def get_distance(self, dist, lookup_type):
         """
         Returns a distance number in units of the field.  For example, if 
         `D(km=1)` was passed in and the units of the field were in meters,
         then 1000 would be returned.
         """
-        
+        postgis = SpatialBackend.name == 'postgis'
         if isinstance(dist, Distance):
-            if self._unit_name in self.geodetic_units:
+            if self.geodetic:
+                # Won't allow Distance objects w/DWithin lookups on PostGIS.
+                if postgis and lookup_type == 'dwithin':
+                    raise TypeError('Only numeric values of degree units are allowed on geographic DWithin queries.')
                 # Spherical distance calculation parameter should be in meters.
                 dist_param = dist.m
             else:
@@ -97,7 +104,7 @@ class GeometryField(SpatialBackend.Field):
             dist_param = dist
 
         # Sphereical distance query; returning meters.
-        if SpatialBackend.name == 'postgis' and self._unit_name in self.geodetic_units:
+        if postgis and self.geodetic and lookup_type != 'dwithin':
             return [gqn(self._spheroid), dist_param]
         else:
             return [dist_param]
@@ -170,7 +177,7 @@ class GeometryField(SpatialBackend.Field):
             if isinstance(value, (tuple, list)):
                 if lookup_type in SpatialBackend.distance_functions:
                     # Getting the distance parameter in the units of the field.
-                    where += self.get_distance(value[1])
+                    where += self.get_distance(value[1], lookup_type)
                 elif lookup_type in SpatialBackend.limited_where:
                     pass
                 else:
diff --git a/django/contrib/gis/tests/distapp/tests.py b/django/contrib/gis/tests/distapp/tests.py
index 0f5b0349dd..3bedb19b4c 100644
--- a/django/contrib/gis/tests/distapp/tests.py
+++ b/django/contrib/gis/tests/distapp/tests.py
@@ -17,7 +17,9 @@ class DistanceTest(unittest.TestCase):
     # the coordinate system of the field, EPSG:32140 (Texas South Central
     # w/units in meters)
     stx_pnt = GEOSGeometry('POINT (-95.370401017314293 29.704867409475465)', 4326)
-    
+    # Another one for Australia
+    au_pnt = GEOSGeometry('POINT (150.791 -34.4919)', 4326)
+
     def get_cities(self, qs):
         cities = [c.name for c in qs]
         cities.sort()
@@ -43,8 +45,17 @@ class DistanceTest(unittest.TestCase):
         dists = [7000, D(km=7), D(mi=4.349)]
         for dist in dists:
             qs = SouthTexasCity.objects.filter(point__dwithin=(self.stx_pnt, dist))
-            cities = self.get_cities(qs)
-            self.assertEqual(cities, ['Downtown Houston', 'Southside Place'])
+            self.assertEqual(['Downtown Houston', 'Southside Place'], self.get_cities(qs))
+
+            if isinstance(dist, D):
+                # A TypeError should be raised when trying to pass Distance objects
+                # into a DWithin query using a geodetic field.
+                qs = AustraliaCity.objects.filter(point__dwithin=(self.au_pnt, dist))
+                self.assertRaises(TypeError, qs.count)
+            else:
+                # Actually using a distance value of 0.5 degrees.
+                qs = AustraliaCity.objects.filter(point__dwithin=(self.au_pnt, 0.5)).order_by('name')
+                self.assertEqual(['Mittagong', 'Shellharbour', 'Thirroul', 'Wollongong'], self.get_cities(qs))
 
     def test03_distance_aggregate(self):
         "Testing the `distance` GeoQuerySet method."