diff --git a/phpunit/tests/fonts/font-library/wpRestFontLibraryController/base.php b/phpunit/tests/fonts/font-library/wpRestFontLibraryController/base.php
index 5caa40b289293..a6b02f38a5e81 100644
--- a/phpunit/tests/fonts/font-library/wpRestFontLibraryController/base.php
+++ b/phpunit/tests/fonts/font-library/wpRestFontLibraryController/base.php
@@ -39,7 +39,7 @@ public function tear_down() {
 		$reflection = new ReflectionClass( 'WP_Font_Library' );
 		$property   = $reflection->getProperty( 'collections' );
 		$property->setAccessible( true );
-		$property->setValue( array() );
+		$property->setValue( null, array() );
 
 		// Clean up the /fonts directory.
 		foreach ( $this->files_in_dir( static::$fonts_dir ) as $file ) {