diff --git a/includes/Api/AbuseLogPrivateDetails.php b/includes/Api/AbuseLogPrivateDetails.php
index 9378eb9a8..53d44f289 100644
--- a/includes/Api/AbuseLogPrivateDetails.php
+++ b/includes/Api/AbuseLogPrivateDetails.php
@@ -124,6 +124,7 @@ class AbuseLogPrivateDetails extends ApiBase {
 			'reason' => [
 				ParamValidator::PARAM_TYPE => 'string',
 				ParamValidator::PARAM_REQUIRED => $this->getConfig()->get( 'AbuseFilterPrivateDetailsForceReason' ),
+				ParamValidator::PARAM_DEFAULT => '',
 			]
 		];
 	}