diff --git a/lib/Instance.js b/lib/Instance.js
index c98f74f4..d0a95b7d 100755
--- a/lib/Instance.js
+++ b/lib/Instance.js
@@ -312,7 +312,7 @@ function Instance(Model, opts) {
 			}
 		}
 
-		for (i = 0; i < opts.extra_info.id; i++) {
+		for (i = 0; i < opts.extra_info.id.length; i++) {
 		    conditions[opts.extra_info.id_prop[i]] = opts.extra_info.id[i];
 		    conditions[opts.extra_info.assoc_prop[i]] = opts.data[opts.id[i]];
 		}