diff --git a/src/database/mongo.js b/src/database/mongo.js
index 253fd78fbe..9862d86571 100644
--- a/src/database/mongo.js
+++ b/src/database/mongo.js
@@ -112,7 +112,7 @@
 					}
 				});
 
-				db.collection('objects').ensureIndex({_key :1, value: -1}, {background:true}, function(err) {
+				db.collection('objects').ensureIndex({_key :1, value: -1}, {background:true, unique: true}, function(err) {
 					if(err) {
 						winston.error('Error creating index ' + err.message);
 					}