diff --git a/fig/service.py b/fig/service.py
index 0648aeb87..bbbef7bc4 100644
--- a/fig/service.py
+++ b/fig/service.py
@@ -251,13 +251,7 @@ class Service(object):
     def start_container(self, container=None, intermediate_container=None, **override_options):
         container = container or self.create_container(**override_options)
         options = dict(self.options, **override_options)
-        ports = {}
-        for port in options.get('ports') or []:
-            internal_port, external = split_port(port)
-            if internal_port in ports:
-                ports[internal_port].append(external)
-            else:
-                ports[internal_port] = [external]
+        port_bindings = build_port_bindings(options.get('ports') or [])
 
         volume_bindings = dict(
             build_volume_binding(parse_volume_spec(volume))
@@ -270,7 +264,7 @@ class Service(object):
 
         container.start(
             links=self._get_links(link_to_self=options.get('one_off', False)),
-            port_bindings=ports,
+            port_bindings=port_bindings,
             binds=volume_bindings,
             volumes_from=self._get_volumes_from(intermediate_container),
             privileged=privileged,
@@ -498,6 +492,17 @@ def build_volume_binding(volume_spec):
     return os.path.abspath(os.path.expandvars(external)), internal
 
 
+def build_port_bindings(ports):
+    port_bindings = {}
+    for port in ports:
+        internal_port, external = split_port(port)
+        if internal_port in port_bindings:
+            port_bindings[internal_port].append(external)
+        else:
+            port_bindings[internal_port] = [external]
+    return port_bindings
+
+
 def split_port(port):
     parts = str(port).split(':')
     if not 1 <= len(parts) <= 3:
diff --git a/tests/unit/service_test.py b/tests/unit/service_test.py
index f1d1c79d9..119b41440 100644
--- a/tests/unit/service_test.py
+++ b/tests/unit/service_test.py
@@ -13,6 +13,7 @@ from fig.container import Container
 from fig.service import (
     ConfigError,
     split_port,
+    build_port_bindings,
     parse_volume_spec,
     build_volume_binding,
     APIError,
@@ -114,6 +115,19 @@ class ServiceTest(unittest.TestCase):
         with self.assertRaises(ConfigError):
             split_port("0.0.0.0:1000:2000:tcp")
 
+    def test_build_port_bindings_with_one_port(self):
+        port_bindings = build_port_bindings(["127.0.0.1:1000:1000"])
+        self.assertEqual(port_bindings["1000"],[("127.0.0.1","1000")])
+
+    def test_build_port_bindings_with_matching_internal_ports(self):
+        port_bindings = build_port_bindings(["127.0.0.1:1000:1000","127.0.0.1:2000:1000"])
+        self.assertEqual(port_bindings["1000"],[("127.0.0.1","1000"),("127.0.0.1","2000")])
+
+    def test_build_port_bindings_with_nonmatching_internal_ports(self):
+        port_bindings = build_port_bindings(["127.0.0.1:1000:1000","127.0.0.1:2000:2000"])
+        self.assertEqual(port_bindings["1000"],[("127.0.0.1","1000")])
+        self.assertEqual(port_bindings["2000"],[("127.0.0.1","2000")])
+
     def test_split_domainname_none(self):
         service = Service('foo', hostname='name', client=self.mock_client)
         self.mock_client.containers.return_value = []