diff --git a/typo3/sysext/core/Tests/Unit/Resource/ResourceCompressorTest.php b/typo3/sysext/core/Tests/Unit/Resource/ResourceCompressorTest.php
index 024c9ea48435499e5f7c01a63d35ec2cb4604971..eff818a332eb1270a93aa76784348ac97c58d051 100644
--- a/typo3/sysext/core/Tests/Unit/Resource/ResourceCompressorTest.php
+++ b/typo3/sysext/core/Tests/Unit/Resource/ResourceCompressorTest.php
@@ -174,7 +174,7 @@ final class ResourceCompressorTest extends UnitTestCase
         $subject = $this->getAccessibleMock(ResourceCompressor::class, ['compressCssFile', 'compressJsFile', 'createMergedCssFile', 'createMergedJsFile', 'getFilenameFromMainDir', 'checkBaseDirectory']);
         $subject->expects(self::exactly(2))
             ->method('createMergedCssFile')
-            ->willReturn(self::returnValue('merged_' . $allFileName), self::returnValue('merged_' . $screenFileName1));
+            ->willReturn('merged_' . $allFileName, 'merged_' . $screenFileName1);
 
         $result = $subject->concatenateCssFiles($testFileFixture);