diff --git a/wp-includes/default-filters.php b/wp-includes/default-filters.php
index d99df1f64..1c69f3805 100644
--- a/wp-includes/default-filters.php
+++ b/wp-includes/default-filters.php
@@ -219,6 +219,7 @@ add_action( 'wp_head',             'wp_shortlink_wp_head',            10, 0 );
 add_action( 'template_redirect',   'wp_shortlink_header',             11, 0 );
 add_action( 'wp_print_footer_scripts', '_wp_footer_scripts'                 );
 add_action( 'init',                'check_theme_switched',            99    );
+add_action( 'after_theme_change',  '_wp_sidebars_changed'                   );
 
 if ( isset( $_GET['replytocom'] ) )
     add_filter( 'pre_option_blog_public', '__return_zero' );
diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index c6d3b3ccc..d30a67992 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -1993,4 +1993,14 @@ function _delete_attachment_theme_mod( $id ) {
 
 add_action( 'delete_attachment', '_delete_attachment_theme_mod' );
 
-?>
+/**
+ * Checks if a theme has been changed and runs 'after_theme_change' hook on the next WP load
+ *
+ * @since 3.3
+ */   
+function check_theme_switched() {
+	if ( false !== ( $old_theme = get_option( 'theme_switched' ) ) && !empty( $old_theme ) ) {
+		do_action( 'after_theme_change', $old_theme );		
+		update_option( 'theme_switched', false );
+	}
+}
diff --git a/wp-includes/widgets.php b/wp-includes/widgets.php
index c2ecd5d20..bc43866fb 100644
--- a/wp-includes/widgets.php
+++ b/wp-includes/widgets.php
@@ -1194,16 +1194,19 @@ function _get_widget_id_base($id) {
 	return preg_replace( '/-[0-9]+$/', '', $id );
 }
 
-function check_theme_switched() {
-	if ( false !== ( $old_theme = get_option( 'theme_switched' ) ) && !empty( $old_theme ) ) {
-		global $sidebars_widgets;
+/**
+ * Handle sidebars config after theme change
+ *
+ * @access private
+ * @since 3.3
+ */  
+function _wp_sidebars_changed() {
+	global $sidebars_widgets;
 
-		if ( ! is_array( $sidebars_widgets ) )
-			$sidebars_widgets = wp_get_sidebars_widgets();
+	if ( ! is_array( $sidebars_widgets ) )
+		$sidebars_widgets = wp_get_sidebars_widgets();
 
-		retrieve_widgets();
-		update_option( 'theme_switched', false );
-	}
+	retrieve_widgets();
 }
 
 // look for "lost" widgets, this has to run at least on each theme change