Index: wp-admin/includes/update.php
===================================================================
--- wp-admin/includes/update.php	(revision 20368)
+++ wp-admin/includes/update.php	(working copy)
@@ -221,9 +221,11 @@
 	$current = get_site_transient('update_themes');
 	$update_themes = array();
 
-	foreach ( $current->response as $stylesheet => $data ) {
-		$update_themes[ $stylesheet ] = wp_get_theme( $stylesheet );
-		$update_themes[ $stylesheet ]->update = $data;
+	if ( isset( $current->response ) ) {
+		foreach ( $current->response as $stylesheet => $data ) {
+			$update_themes[ $stylesheet ] = wp_get_theme( $stylesheet );
+			$update_themes[ $stylesheet ]->update = $data;
+		}
 	}
 
 	return $update_themes;