diff --git a/setup.cfg b/setup.cfg
index 763992b..fca70c6 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -107,6 +107,8 @@ no_implicit_optional = true
 warn_unused_ignores = true
 
 # TODO: until we opt in all the modules
+[mypy-flake8.__init__]
+disallow_untyped_defs = true
 [mypy-flake8.defaults]
 disallow_untyped_defs = true
 [mypy-flake8.exceptions]
diff --git a/src/flake8/__init__.py b/src/flake8/__init__.py
index 6b40748..53bc407 100644
--- a/src/flake8/__init__.py
+++ b/src/flake8/__init__.py
@@ -11,6 +11,7 @@ This module
 """
 import logging
 import sys
+from typing import Optional
 from typing import Type
 
 LOG = logging.getLogger(__name__)
@@ -40,7 +41,11 @@ LOG_FORMAT = (
 )
 
 
-def configure_logging(verbosity, filename=None, logformat=LOG_FORMAT):
+def configure_logging(
+    verbosity: int,
+    filename: Optional[str] = None,
+    logformat: str = LOG_FORMAT,
+) -> None:
     """Configure logging for flake8.
 
     :param int verbosity: