diff --git a/tests/phpunit/includes/testcase-ajax.php b/tests/phpunit/includes/testcase-ajax.php
index 2227413511..76ceb73af1 100644
--- a/tests/phpunit/includes/testcase-ajax.php
+++ b/tests/phpunit/includes/testcase-ajax.php
@@ -59,8 +59,6 @@ abstract class WP_Ajax_UnitTestCase extends WP_UnitTestCase {
 	);
 
 	public static function setUpBeforeClass() {
-		add_filter( 'wp_doing_ajax', '__return_true' );		
-
 		remove_action( 'admin_init', '_maybe_update_core' );
 		remove_action( 'admin_init', '_maybe_update_plugins' );
 		remove_action( 'admin_init', '_maybe_update_themes' );
@@ -82,6 +80,7 @@ abstract class WP_Ajax_UnitTestCase extends WP_UnitTestCase {
 	public function setUp() {
 		parent::setUp();
 
+		add_filter( 'wp_doing_ajax', '__return_true' );
 		add_filter( 'wp_die_ajax_handler', array( $this, 'getDieHandler' ), 1, 1 );
 
 		set_current_screen( 'ajax' );