diff --git a/geopandas/geodataframe.py b/geopandas/geodataframe.py
index 08c8a3d..49e7691 100644
--- a/geopandas/geodataframe.py
+++ b/geopandas/geodataframe.py
@@ -461,10 +461,9 @@ class GeoDataFrame(GeoPandasBase, DataFrame):
         # Separate data and geometry
         data = self.drop(labels=self.geometry.name, axis=1).copy()
 
-
-        groupby_plus_geometry = [self.geometry.name]
-        groupby_plus_geometry.append(by)
-        geometry = self[groupby_plus_geometry].copy()
+        groupby_plus_geometry_cols = [self.geometry.name]
+        groupby_plus_geometry_cols.append(by)
+        geometry = self[groupby_plus_geometry_cols].copy()
 
         # Process data
         aggregated_data = data.groupby(by=by).agg(aggfunc)
diff --git a/tests/test_dissolve.py b/tests/test_dissolve.py
index 8bac2ba..a0569d0 100644
--- a/tests/test_dissolve.py
+++ b/tests/test_dissolve.py
@@ -5,7 +5,8 @@ from shapely.geometry import Point
 from geopandas import GeoDataFrame, read_file
 from geopandas.tools import overlay
 from .util import unittest, download_nybb
-
+from pandas.util.testing import assert_frame_equal
+from pandas import Index
 
 class TestDataFrame(unittest.TestCase):
 
@@ -13,28 +14,39 @@ class TestDataFrame(unittest.TestCase):
 
         nybb_filename, nybb_zip_path = download_nybb()
         self.polydf = read_file(nybb_zip_path, vfs='zip://' + nybb_filename)
+        self.polydf = self.polydf[['geometry', 'BoroName', 'BoroCode']]
 
         self.polydf = self.polydf.rename(columns={'geometry':'myshapes'})
         self.polydf = self.polydf.set_geometry('myshapes')
 
-        self.polydf['manhattan_bronx'] = 0
-        self.polydf.loc[3:4,'manhattan_bronx']=1
+        self.polydf['manhattan_bronx'] = 5
+        self.polydf.loc[3:4,'manhattan_bronx']=6
 
         # Merged geometry
         manhattan_bronx = self.polydf.loc[3:4,]
         others = self.polydf.loc[0:2,]
-        
 
-        self.merged_shapes = GeoDataFrame(columns=manhattan_bronx.columns)
-        self.merged_shapes.loc[0, 'myshapes'] = others.geometry.unary_union
-        self.merged_shapes.loc[1, 'myshapes'] = manhattan_bronx.geometry.unary_union
-        self.merged_shapes = self.merged_shapes.set_geometry('myshapes')
+        collapsed = [others.geometry.unary_union, manhattan_bronx.geometry.unary_union]
+        merged_shapes = GeoDataFrame({'myshapes': collapsed}, geometry='myshapes', 
+                             index=Index([5,6], name='manhattan_bronx'))
+
+        # Different expected results
+        self.first = merged_shapes.copy()
+        self.first['BoroName'] = ['Staten Island', 'Manhattan']
+        self.first['BoroCode'] = [5, 1]
+
+        self.mean = merged_shapes.copy()
+        self.mean['BoroCode'] = [4,1.5]
+
 
     def test_geom_dissolve(self):
         test = self.polydf.dissolve('manhattan_bronx')
         self.assertTrue(test.geometry.name == 'myshapes')
+        self.assertTrue(test.geom_almost_equals(self.first).all())
 
-        known = self.merged_shapes.geometry
-        self.assertTrue(test.geometry.geom_almost_equals(known).all())
-
+    def test_first_dissolve(self):
+        test = self.polydf.dissolve('manhattan_bronx')
+        test = test.drop('myshapes', axis=1)
+        first = self.first.drop('myshapes', axis=1)
+        assert_frame_equal(first, test)