Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 17805)
+++ wp-includes/query.php	(working copy)
@@ -2462,9 +2462,14 @@
 
 		// Parse the meta query again if query vars have changed.
 		if ( $this->query_vars_changed ) {
-			$meta_query_hash = md5( serialize( $q['meta_query'] ) );
-			$_meta_query = $q['meta_query'];
-			unset( $q['meta_query'] );
+			if ( isset( $q['meta_query'] ) ) {
+				$meta_query_hash = md5( serialize( $q['meta_query'] ) );
+				$_meta_query = $q['meta_query'];
+				unset( $q['meta_query'] );
+			} else {
+				$meta_query_hash = false;
+				$_meta_query = array();
+			}
 			_parse_meta_query( $q );
 			if ( md5( serialize( $q['meta_query'] ) ) != $meta_query_hash && is_array( $_meta_query ) )
 				$q['meta_query'] = array_merge( $_meta_query, $q['meta_query'] );