diff --git a/appengine/standard_python3/custom-server/requirements.txt b/appengine/standard_python3/custom-server/requirements.txt
index 9a9e615f963..45acdb369aa 100644
--- a/appengine/standard_python3/custom-server/requirements.txt
+++ b/appengine/standard_python3/custom-server/requirements.txt
@@ -1,2 +1,2 @@
 uwsgi==2.0.20
-flask==2.1.0
+flask==2.3.2