diff --git a/setup.py b/setup.py
index 5b56aad..04d61f5 100644
--- a/setup.py
+++ b/setup.py
@@ -16,5 +16,5 @@
     package_dir={"": "src"},
     packages=["cs50"],
     url="https://github.com/cs50/python-cs50",
-    version="4.0.0"
+    version="4.0.1"
 )
diff --git a/src/cs50/flask.py b/src/cs50/flask.py
index a20d53c..2ab0ba2 100644
--- a/src/cs50/flask.py
+++ b/src/cs50/flask.py
@@ -49,8 +49,8 @@ def _after(*args, **kwargs):
             import flask
             from werkzeug.middleware.proxy_fix import ProxyFix
             _before = flask.Flask.__init__
-            def _after(*args, **kwargs):
-                _before(*args, **kwargs)
+            def _after(self, *args, **kwargs):
+                _before(self, *args, **kwargs)
                 self.wsgi_app = ProxyFix(self.wsgi_app, x_proto=1)
             flask.Flask.__init__ = _after
         except: