diff --git a/docker/api/container.py b/docker/api/container.py
index 338b79fe..b4363532 100644
--- a/docker/api/container.py
+++ b/docker/api/container.py
@@ -100,7 +100,7 @@ class ContainerApiMixin(object):
                 DeprecationWarning
             )
         res = self._post_json(
-            self._url("/containers/{0}/copy".format(container)),
+            self._url("/containers/{0}/copy", container),
             data={"Resource": resource},
             stream=True
         )