diff --git a/lib/User/Backend.php b/lib/User/Backend.php
index f5924ce4..37a5793d 100644
--- a/lib/User/Backend.php
+++ b/lib/User/Backend.php
@@ -230,6 +230,12 @@ public function getCurrentUserId(): string {
 			return '';
 		}
 
+		$tks = \explode('.', $headerToken);
+        if (\count($tks) !== 3) {
+			$this->logger->debug('Bearer token is no JWT');
+			return '';
+		}
+
 		$oidcSystemConfig = $this->config->getSystemValue('user_oidc', []);
 		// check if we should use UserInfoValidator (default is false)
 		if (!isset($oidcSystemConfig['userinfo_bearer_validation']) || !$oidcSystemConfig['userinfo_bearer_validation']) {