diff --git a/authlib/integrations/flask_client/apps.py b/authlib/integrations/flask_client/apps.py
index 7567f4b3..84ac8c0d 100644
--- a/authlib/integrations/flask_client/apps.py
+++ b/authlib/integrations/flask_client/apps.py
@@ -85,12 +85,12 @@ def authorize_access_token(self, **kwargs):
                 raise OAuthError(error=error, description=description)
 
             params = {
-                'code': request.args['code'],
+                'code': request.args.get('code'),
                 'state': request.args.get('state'),
             }
         else:
             params = {
-                'code': request.form['code'],
+                'code': request.form.get('code'),
                 'state': request.form.get('state'),
             }