diff --git a/compose/config/config.py b/compose/config/config.py
index e08b503f3..b7697f002 100644
--- a/compose/config/config.py
+++ b/compose/config/config.py
@@ -151,7 +151,7 @@ def load(config_details):
 
 
 class ServiceLoader(object):
-    def __init__(self, working_dir, filename=None, already_seen=None):
+    def __init__(self, working_dir, filename, already_seen=None):
         if working_dir is None:
             raise Exception("No working_dir passed to ServiceLoader()")
 
diff --git a/tests/integration/testcases.py b/tests/integration/testcases.py
index 08ef9f272..d9d666d27 100644
--- a/tests/integration/testcases.py
+++ b/tests/integration/testcases.py
@@ -31,7 +31,7 @@ class DockerClientTestCase(unittest.TestCase):
         if 'command' not in kwargs:
             kwargs['command'] = ["top"]
 
-        options = ServiceLoader(working_dir='.').make_service_dict(name, kwargs)
+        options = ServiceLoader(working_dir='.', filename=None).make_service_dict(name, kwargs)
 
         labels = options.setdefault('labels', {})
         labels['com.docker.compose.test-name'] = self.id()
diff --git a/tests/unit/config_test.py b/tests/unit/config_test.py
index e488ceb52..aa10982b4 100644
--- a/tests/unit/config_test.py
+++ b/tests/unit/config_test.py
@@ -11,11 +11,11 @@ from compose.config import config
 from compose.config.errors import ConfigurationError
 
 
-def make_service_dict(name, service_dict, working_dir):
+def make_service_dict(name, service_dict, working_dir, filename=None):
     """
     Test helper function to construct a ServiceLoader
     """
-    return config.ServiceLoader(working_dir=working_dir).make_service_dict(name, service_dict)
+    return config.ServiceLoader(working_dir=working_dir, filename=filename).make_service_dict(name, service_dict)
 
 
 def service_sort(services):