diff --git a/src/wp-includes/theme.php b/src/wp-includes/theme.php
index 89eab5f790..6909d0fe2e 100644
--- a/src/wp-includes/theme.php
+++ b/src/wp-includes/theme.php
@@ -690,7 +690,7 @@ function switch_theme( $stylesheet ) {
 	}
 
 	if ( is_array( $_sidebars_widgets ) ) {
-		set_theme_mod( 'sidebars_widgets', $_sidebars_widgets );
+		set_theme_mod( 'sidebars_widgets', array( 'time' => time(), 'data' => $_sidebars_widgets ) );
 	}
 
 	$nav_menu_locations = get_theme_mod( 'nav_menu_locations' );
diff --git a/src/wp-includes/widgets.php b/src/wp-includes/widgets.php
index 37e8a01c52..6f5954d322 100644
--- a/src/wp-includes/widgets.php
+++ b/src/wp-includes/widgets.php
@@ -1286,6 +1286,7 @@ function wp_map_sidebars_widgets( $existing_sidebars_widgets ) {
 
 	// Sidebars_widgets settings from when this theme was previously active.
 	$old_sidebars_widgets = get_theme_mod( 'sidebars_widgets' );
+	$old_sidebars_widgets = $old_sidebars_widgets['data'];
 
 	if ( is_array( $old_sidebars_widgets ) ) {
 
diff --git a/tests/phpunit/tests/widgets.php b/tests/phpunit/tests/widgets.php
index a56caefb95..c37dcc08a0 100644
--- a/tests/phpunit/tests/widgets.php
+++ b/tests/phpunit/tests/widgets.php
@@ -713,10 +713,13 @@ class Tests_Widgets extends WP_UnitTestCase {
 
 		// Test restoring sidebars widgets when previously activated.
 		set_theme_mod( 'sidebars_widgets', array(
-			'sidebar-1' => array( 'tag_cloud-1' ),
-			'sidebar-2' => array(),
-			'sidebar-3' => array( 'unregistered_widget-1', 'text-1', 'media_image-1' ),
-			'orphaned_widgets_1' => array( 'media_video-2' ),
+			'time' => time(),
+			'data' => array(
+				'sidebar-1' => array( 'tag_cloud-1' ),
+				'sidebar-2' => array(),
+				'sidebar-3' => array( 'unregistered_widget-1', 'text-1', 'media_image-1' ),
+				'orphaned_widgets_1' => array( 'media_video-2' ),
+			),
 		) );
 
 		$sidebars_widgets = array(