diff --git a/tests/phpunit/ApiQueryPageImagesProxyMock.php b/tests/phpunit/ApiQueryPageImagesProxyMock.php
index ffa01d2..f029d90 100644
--- a/tests/phpunit/ApiQueryPageImagesProxyMock.php
+++ b/tests/phpunit/ApiQueryPageImagesProxyMock.php
@@ -7,6 +7,8 @@ use PageImages\ApiQueryPageImages;
 
 class ApiQueryPageImagesProxyMock extends ApiQueryPageImages {
 
+	private ApiPageSet $pageSet;
+
 	/** @inheritDoc */
 	public function __construct( ApiPageSet $pageSet ) {
 		$this->pageSet = $pageSet;