diff --git a/src/LtiMessageLaunch.php b/src/LtiMessageLaunch.php
index cf0b1bf7..ff816b64 100644
--- a/src/LtiMessageLaunch.php
+++ b/src/LtiMessageLaunch.php
@@ -283,7 +283,7 @@ public function getLaunchId()
         return $this->launch_id;
     }
 
-    public function getMissingRegistrationErrorMsg(string $issuerUrl, string $clientId): string
+    public static function getMissingRegistrationErrorMsg(string $issuerUrl, string $clientId): string
     {
         $search = [':issuerUrl', ':clientId'];
         $replace = [$issuerUrl, $clientId];