Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 11829)
+++ wp-includes/query.php	(working copy)
@@ -2146,10 +2146,18 @@
 		if ( ! empty($q['meta_key']) )
 			$where .= $wpdb->prepare(" AND $wpdb->postmeta.meta_key = %s ", $q['meta_key']);
 		if ( ! empty($q['meta_value']) ) {
-			if ( ! isset($q['meta_compare']) || empty($q['meta_compare']) || ! in_array($q['meta_compare'], array('=', '!=', '>', '>=', '<', '<=')) )
+			if ( ! isset($q['meta_compare']) || empty($q['meta_compare']) || ! in_array($q['meta_compare'], array('=', '!=', '>', '>=', '<', '<=', 'in')) )
 				$q['meta_compare'] = '=';
-
-			$where .= $wpdb->prepare("AND $wpdb->postmeta.meta_value {$q['meta_compare']} %s ", $q['meta_value']);
+			if ( 'in' == $q['meta_compare'] ) {
+				if ( !is_array($q['meta_value']) )
+					$q['meta_value'] = preg_split('!,\s+!', $q['meta_value']);
+				$meta_field_types = rtrim(str_repeat('%s,', count($q['meta_value'])), ',');
+				$where .= $wpdb->prepare("AND $wpdb->postmeta.meta_value IN($meta_field_types) ", $q['meta_value']);
+				unset($meta_field_types);
+			} else {
+				$where .= $wpdb->prepare("AND $wpdb->postmeta.meta_value {$q['meta_compare']} %s ", $q['meta_value']);
+			}
+
 		}
 
 		// Apply filters on where and join prior to paging so that any