diff --git a/compose/config/types.py b/compose/config/types.py
index 6d3ca3f3b..4509bfe67 100644
--- a/compose/config/types.py
+++ b/compose/config/types.py
@@ -325,7 +325,7 @@ class ServicePort(namedtuple('_ServicePort', 'target published protocol mode ext
 
     @property
     def merge_field(self):
-        return (self.target, self.published)
+        return (self.target, self.published, self.external_ip, self.protocol)
 
     def repr(self):
         return dict(
diff --git a/tests/unit/config/config_test.py b/tests/unit/config/config_test.py
index d92a35c00..87bdd8bca 100644
--- a/tests/unit/config/config_test.py
+++ b/tests/unit/config/config_test.py
@@ -1865,7 +1865,7 @@ class ConfigTest(unittest.TestCase):
                 {
                     'target': '1245',
                     'published': '1245',
-                    'protocol': 'tcp',
+                    'protocol': 'udp',
                 }
             ]
         }