diff --git a/wp-includes/class-wp-customize-manager.php b/wp-includes/class-wp-customize-manager.php
index d159458a78..a51d035eaf 100644
--- a/wp-includes/class-wp-customize-manager.php
+++ b/wp-includes/class-wp-customize-manager.php
@@ -424,7 +424,7 @@ final class WP_Customize_Manager {
 	 * @since 3.4.0
 	 */
 	public function after_setup_theme() {
-		$doing_ajax_or_is_customized = ( $this->doing_ajax() || isset( $_SERVER['customized'] ) );
+		$doing_ajax_or_is_customized = ( $this->doing_ajax() || isset( $_POST['customized'] ) );
 		if ( ! $doing_ajax_or_is_customized && ! validate_current_theme() ) {
 			wp_redirect( 'themes.php?broken=true' );
 			exit;
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 0b423203c3..d9c2294428 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.6-alpha-37519';
+$wp_version = '4.6-alpha-37520';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.