diff --git a/UPGRADE.md b/UPGRADE.md
index 84dc7d83..5ad81992 100644
--- a/UPGRADE.md
+++ b/UPGRADE.md
@@ -1,5 +1,8 @@
 # Upgrade Notes
 
+## 5.3.2
+- **[BUGFIX]** Validate and cast formId to integer in RequestListener
+
 ## 5.3.1
 - **[BUGFIX]** [FUNNEL] Add channel context handling to FunnelWorker [#518](https://github.com/dachcom-digital/pimcore-formbuilder/issues/518)
 - **[BUGFIX]** [FUNNEL] Render `_token` in funnel base template if available and renderable
diff --git a/src/EventListener/Core/RequestListener.php b/src/EventListener/Core/RequestListener.php
index 67dd848a..71fed19e 100644
--- a/src/EventListener/Core/RequestListener.php
+++ b/src/EventListener/Core/RequestListener.php
@@ -229,7 +229,7 @@ protected function detectFormIdByType(array $values, string $formMatchType = sel
             }
 
             if (isset($parameters['formId'])) {
-                return $parameters['formId'];
+                return is_numeric($parameters['formId']) ? (int) $parameters['formId'] : null;
             }
         }