diff --git a/docs/patterns/fileuploads.rst b/docs/patterns/fileuploads.rst
index 95c0032f91..8ab8c033dd 100644
--- a/docs/patterns/fileuploads.rst
+++ b/docs/patterns/fileuploads.rst
@@ -47,7 +47,7 @@ the file and redirects the user to the URL for the uploaded file::
 
     def allowed_file(filename):
         return '.' in filename and \
-               filename.rsplit('.', 1)[1] in ALLOWED_EXTENSIONS
+               filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS
 
     @app.route('/', methods=['GET', 'POST'])
     def upload_file():