diff --git a/tests/phpunit/includes/testcase-ajax.php b/tests/phpunit/includes/testcase-ajax.php
index e48647201f..b415976f21 100644
--- a/tests/phpunit/includes/testcase-ajax.php
+++ b/tests/phpunit/includes/testcase-ajax.php
@@ -50,21 +50,6 @@ abstract class WP_Ajax_UnitTestCase extends WP_UnitTestCase {
 		'wp-remove-post-lock', 'dismiss-wp-pointer', 'heartbeat', 'nopriv_heartbeat',
 	);
 
-	/**
-	 * Don't preserve the global state when using an external object cache.
-	 *
-	 * Most of the Ajax tests are running in a separate PHP process, and thus PHPUnit attempts
-	 * to preserve the global state from the parent process by serializing all globals.
-	 * But this doesn't work for external object caches so we have to disable this "feature".
-	 */
-	public function run( PHPUnit_Framework_TestResult $result = NULL ) {
-		if ( wp_using_ext_object_cache() ) {
-			$this->setPreserveGlobalState( false );
-		}
-
-		return parent::run( $result );
-	}
-
 	/**
 	 * Set up the test fixture.
 	 * Override wp_die(), pretend to be ajax, and suppres E_WARNINGs
diff --git a/tests/phpunit/tests/ajax/Autosave.php b/tests/phpunit/tests/ajax/Autosave.php
index 512cbbd6e5..33cd79f1ba 100644
--- a/tests/phpunit/tests/ajax/Autosave.php
+++ b/tests/phpunit/tests/ajax/Autosave.php
@@ -12,7 +12,6 @@ require_once( ABSPATH . 'wp-admin/includes/ajax-actions.php' );
  * @subpackage UnitTests
  * @since      3.4.0
  * @group      ajax
- * @runTestsInSeparateProcesses
  */
 class Tests_Ajax_Autosave extends WP_Ajax_UnitTestCase {
 
diff --git a/tests/phpunit/tests/ajax/Compression.php b/tests/phpunit/tests/ajax/Compression.php
index d8d5235644..475c206807 100644
--- a/tests/phpunit/tests/ajax/Compression.php
+++ b/tests/phpunit/tests/ajax/Compression.php
@@ -12,7 +12,6 @@ require_once( ABSPATH . 'wp-admin/includes/ajax-actions.php' );
  * @subpackage UnitTests
  * @since      3.4.0
  * @group      ajax
- * @runTestsInSeparateProcesses
  */
 class Tests_Ajax_CompressionTest extends WP_Ajax_UnitTestCase {
 
diff --git a/tests/phpunit/tests/ajax/CustomizeMenus.php b/tests/phpunit/tests/ajax/CustomizeMenus.php
index 135929756c..eb0fb3b9dd 100644
--- a/tests/phpunit/tests/ajax/CustomizeMenus.php
+++ b/tests/phpunit/tests/ajax/CustomizeMenus.php
@@ -6,7 +6,6 @@
  * @subpackage UnitTests
  * @since      4.3.0
  * @group      ajax
- * @runTestsInSeparateProcesses
  */
 class Tests_Ajax_CustomizeMenus extends WP_Ajax_UnitTestCase {
 
diff --git a/tests/phpunit/tests/ajax/Response.php b/tests/phpunit/tests/ajax/Response.php
index 9c48a8161d..bc99341fb0 100644
--- a/tests/phpunit/tests/ajax/Response.php
+++ b/tests/phpunit/tests/ajax/Response.php
@@ -6,7 +6,6 @@
  * @subpackage UnitTests
  * @since      3.5.0
  * @group      ajax
- * @runInSeparateProcess
  */
 class Tests_Ajax_Response extends WP_UnitTestCase {
 
@@ -65,6 +64,8 @@ class Tests_Ajax_Response extends WP_UnitTestCase {
 	 * Needs a separate process to get around the headers/output from the
 	 * bootstrapper
 	 * @ticket 19448
+	 * @runInSeparateProcess
+	 * @preserveGlobalState disabled
 	 */
 	public function test_response_charset_in_header() {