diff --git a/docker/types/services.py b/docker/types/services.py
index 821115411..fd831dd55 100644
--- a/docker/types/services.py
+++ b/docker/types/services.py
@@ -560,11 +560,9 @@ def __init__(self, mode=None, ports=None):
 
 
 def convert_service_ports(ports):
-    if isinstance(ports, list):
-        return ports
     if not isinstance(ports, dict):
         raise TypeError(
-            'Invalid type for ports, expected dict or list'
+            'Invalid type for ports, expected dict'
         )
 
     result = []
diff --git a/tests/unit/dockertypes_test.py b/tests/unit/dockertypes_test.py
index 03e7d2eda..c6b3e1932 100644
--- a/tests/unit/dockertypes_test.py
+++ b/tests/unit/dockertypes_test.py
@@ -491,3 +491,9 @@ def test_convert_service_ports_multiple(self):
         } in converted_ports
 
         assert len(converted_ports) == 3
+
+    def test_convert_service_ports_wrong_ports_type(self):
+        ports = 'ports_as_string'
+
+        with pytest.raises(TypeError):
+            convert_service_ports(ports)