diff --git a/pre_commit_hooks/forbid_new_submodules.py b/pre_commit_hooks/forbid_new_submodules.py
index c9464cf..bdbd6f7 100644
--- a/pre_commit_hooks/forbid_new_submodules.py
+++ b/pre_commit_hooks/forbid_new_submodules.py
@@ -2,10 +2,13 @@
 from __future__ import print_function
 from __future__ import unicode_literals
 
+from typing import Optional
+from typing import Sequence
+
 from pre_commit_hooks.util import cmd_output
 
 
-def main(argv=None):
+def main(argv=None):  # type: (Optional[Sequence[str]]) -> int
     # `argv` is ignored, pre-commit will send us a list of files that we
     # don't care about
     added_diff = cmd_output(