diff --git a/wp-admin/customize.php b/wp-admin/customize.php
index 29ae035599..7e69d13488 100644
--- a/wp-admin/customize.php
+++ b/wp-admin/customize.php
@@ -12,16 +12,20 @@ define( 'IFRAME_REQUEST', true );
 /** Load WordPress Administration Bootstrap */
 require_once( dirname( __FILE__ ) . '/admin.php' );
 
-if ( ! current_user_can( 'edit_theme_options' ) )
+if ( ! current_user_can( 'edit_theme_options' ) ) {
 	wp_die( __( 'Cheatin’ uh?' ) );
+}
 
 wp_reset_vars( array( 'url', 'return' ) );
-$url = urldecode( $url );
+$url = wp_unslash( $url );
 $url = wp_validate_redirect( $url, home_url( '/' ) );
-if ( $return )
-	$return = wp_validate_redirect( urldecode( $return ) );
-if ( ! $return )
+if ( $return ) {
+	$return = wp_unslash( $return );
+	$return = wp_validate_redirect( $return );
+}
+if ( ! $return ) {
 	$return = $url;
+}
 
 global $wp_scripts, $wp_customize;
 
diff --git a/wp-admin/menu.php b/wp-admin/menu.php
index 4008a0986d..4910fd456a 100644
--- a/wp-admin/menu.php
+++ b/wp-admin/menu.php
@@ -146,9 +146,13 @@ $appearance_cap = current_user_can( 'switch_themes') ? 'switch_themes' : 'edit_t
 
 $menu[60] = array( __('Appearance'), $appearance_cap, 'themes.php', '', 'menu-top menu-icon-appearance', 'menu-appearance', 'dashicons-admin-appearance' );
 	$submenu['themes.php'][5] = array( __( 'Themes' ), $appearance_cap, 'themes.php' );
-	$submenu['themes.php'][6] = array( __( 'Customize' ), 'edit_theme_options', 'customize.php', 'hide-if-no-customize' );
-	if ( current_theme_supports( 'menus' ) || current_theme_supports( 'widgets' ) )
+
+	$customize_url = add_query_arg( 'return', urlencode( wp_unslash( $_SERVER['REQUEST_URI'] ) ), 'customize.php' );
+	$submenu['themes.php'][6] = array( __( 'Customize' ), 'edit_theme_options', $customize_url, 'hide-if-no-customize' );
+	unset( $customize_url );
+	if ( current_theme_supports( 'menus' ) || current_theme_supports( 'widgets' ) ) {
 		$submenu['themes.php'][10] = array(__( 'Menus' ), 'edit_theme_options', 'nav-menus.php');
+	}
 
 unset( $appearance_cap );