diff --git a/app-code/api/account/update_passkey.php b/app-code/api/account/update_passkey.php
index d0fa7c7..5adedf0 100644
--- a/app-code/api/account/update_passkey.php
+++ b/app-code/api/account/update_passkey.php
@@ -166,7 +166,7 @@ try {
         $data->userDisplayName = $userDisplayName;
 
         // Store registration data in the database
-	$credentialId = $data->credentialId;
+	$credentialId = $data->credentialId instanceof \lbuchs\WebAuthn\Binary\ByteBuffer ? $data->credentialId->getBinaryString() : $data->credentialId;
 	$credentialPublicKey = $data->credentialPublicKey;
 	$signatureCounter = (int)$data->signatureCounter;
 	$stmt = $conn->prepare("UPDATE users set  credential_id = ?, public_key = ?, counter = ?, auth_method_enabled_passkey = 1, auth_method_required_passkey = 1 WHERE username = ?");