diff --git a/ansible_mitogen/helpers.py b/ansible_mitogen/helpers.py
index 50dd3cec..9e8693d9 100644
--- a/ansible_mitogen/helpers.py
+++ b/ansible_mitogen/helpers.py
@@ -174,7 +174,7 @@ def _async_main(job_id, module, raw_params, args, env):
     _result_by_job_id[job_id] = rc
 
 
-def make_temp_directory:(base_dir):
+def make_temp_directory(base_dir):
     """
     Handle creation of `base_dir` if it is absent, in addition to a unique
     temporary directory within `base_dir`.
diff --git a/ansible_mitogen/mixins.py b/ansible_mitogen/mixins.py
index 151358f9..9cef0c3e 100644
--- a/ansible_mitogen/mixins.py
+++ b/ansible_mitogen/mixins.py
@@ -203,7 +203,7 @@ class ActionModuleMixin(ansible.plugins.action.ActionBase):
         # The copy action plugin violates layering and grabs this attribute
         # directly.
         self._connection._shell.tmpdir = self.call(
-            ansible_mitogen.helpers.make_temp_directory:,
+            ansible_mitogen.helpers.make_temp_directory,
             base_dir=self._remote_expand_user(
                 # ~/.ansible
                 self._connection._shell.get_option('remote_tmp')