Index: wp-includes/wp-db.php
===================================================================
--- wp-includes/wp-db.php	(revision 13947)
+++ wp-includes/wp-db.php	(working copy)
@@ -624,9 +624,11 @@
 	 * @param int $blog_id Optional.
 	 * @return string Blog prefix.
 	 */
-	function get_blog_prefix( $blog_id = 0 ) {
-		if ( is_multisite() && $blog_id ) {
-			if ( defined( 'MULTISITE' ) && ( 0 == $blog_id || 1 == $blog_id ) )
+	function get_blog_prefix( $blog_id = null ) {
+		if ( is_multisite() ) {
+			if ( null === $blog_id )
+				return $this->prefix; // Return prefix for the current blog if no ID is given.
+			elseif ( defined( 'MULTISITE' ) && ( 0 == $blog_id || 1 == $blog_id ) )
 				return $this->base_prefix;
 			else
 				return $this->base_prefix . $blog_id . '_';