diff --git a/src/Signer/Ecdsa.php b/src/Signer/Ecdsa.php
index 472cbbad..7291890a 100644
--- a/src/Signer/Ecdsa.php
+++ b/src/Signer/Ecdsa.php
@@ -56,6 +56,7 @@ final protected function guardAgainstIncompatibleKey(int $type, int $lengthInBit
         }
     }
 
+    /** @internal */
     abstract public function expectedKeyLength(): int;
 
     /**