diff --git a/magnumclient/common/utils.py b/magnumclient/common/utils.py
index 4c40bc3..9c26ac7 100644
--- a/magnumclient/common/utils.py
+++ b/magnumclient/common/utils.py
@@ -112,9 +112,7 @@ def format_labels(lbls, parse_comma=True):
         if k not in labels:
             labels[k] = v
         else:
-            if not isinstance(labels[k], list):
-                labels[k] = [labels[k]]
-            labels[k].append(v)
+            labels[k] += ",%s" % v
 
     return labels
 
diff --git a/magnumclient/tests/test_utils.py b/magnumclient/tests/test_utils.py
index d263201..7bef020 100644
--- a/magnumclient/tests/test_utils.py
+++ b/magnumclient/tests/test_utils.py
@@ -191,9 +191,7 @@ class FormatLabelsTest(test_utils.BaseTestCase):
         l = utils.format_labels([
             'K1=V1',
             'K1=V2'])
-        self.assertIn('K1', l)
-        self.assertIn('V1', l['K1'])
-        self.assertIn('V2', l['K1'])
+        self.assertEqual({'K1': 'V1,V2'}, l)
 
     def test_format_label_special_label(self):
         labels = ['K1=V1,K22.2.2.2']