diff --git a/wp-includes/wp-db.php b/wp-includes/wp-db.php
index 4b65069876..d6e844d9d3 100644
--- a/wp-includes/wp-db.php
+++ b/wp-includes/wp-db.php
@@ -489,12 +489,11 @@ class wpdb {
 	}
 
 	function get_blog_prefix( $blog_id = '' ) {
-		if ( $blog_id ) {
-                        if( defined('MULTISITE') && ( $blog_id == 0 || $blog_id == 1) ) {
-        			return $this->base_prefix;
-                        } else {
-        			return $this->base_prefix . $blog_id . '_';
-                        }
+		if ( is_multisite() && $blog_id ) {
+			if ( defined('MULTISITE') && ( $blog_id == 0 || $blog_id == 1 ) )
+				return $this->base_prefix;
+			else
+				return $this->base_prefix . $blog_id . '_';
 		} else {
 			return $this->base_prefix;
 		}