diff --git a/next.config.mjs b/next.config.mjs
index 792d21f1..69ce52be 100644
--- a/next.config.mjs
+++ b/next.config.mjs
@@ -16,7 +16,7 @@ const disableLogin = process.env.DISABLE_LOGIN;
 const disableUI = process.env.DISABLE_UI;
 const faviconURL = process.env.FAVICON_URL;
 const forceSSL = process.env.FORCE_SSL;
-const frameAncestors = process.env.ALLOWED_FRAME_URLS;
+const frameAncestors = process.env.ALLOWED_FRAME_URLS ?? '';
 const privateMode = process.env.PRIVATE_MODE;
 const trackerScriptName = process.env.TRACKER_SCRIPT_NAME;
 const trackerScriptURL = process.env.TRACKER_SCRIPT_URL;