diff --git a/js/server/modules/@arangodb/cluster.js b/js/server/modules/@arangodb/cluster.js
index ea64eda596..a1b964c43c 100644
--- a/js/server/modules/@arangodb/cluster.js
+++ b/js/server/modules/@arangodb/cluster.js
@@ -1229,6 +1229,9 @@ function scheduleOneShardSynchronization (database, shard, planId, leader) {
 
 function synchronizeLocalFollowerCollections (plannedCollections,
   currentCollections) {
+  if (typeof currentCollections != 'object') {
+    throw new Error('Current.Collections is not an object!');
+  }
   var ourselves = global.ArangoServerState.id();
 
   var db = require('internal').db;