diff --git a/js/server/modules/@arangodb/cluster.js b/js/server/modules/@arangodb/cluster.js
index 721fc1d92c..1351eea08d 100644
--- a/js/server/modules/@arangodb/cluster.js
+++ b/js/server/modules/@arangodb/cluster.js
@@ -34,6 +34,7 @@ var ArangoCollection = arangodb.ArangoCollection;
 var ArangoError = arangodb.ArangoError;
 var request = require("@arangodb/request").request;
 var wait = require("internal").wait;
+var _ = require("lodash");
 
 var endpointToURL = function (endpoint) {
   if (endpoint.substr(0,6) === "ssl://") {
@@ -969,14 +970,21 @@ function launchJob() {
     var shards = Object.keys(jobs.scheduled);
     if (shards.length > 0) {
       var jobInfo = jobs.scheduled[shards[0]];
-      registerTask({
-        database: jobInfo.database,
-        params: {database: jobInfo.database, shard: jobInfo.shard, 
-                 planId: jobInfo.planId, leader: jobInfo.leader},
-        command: function(params) {
-          require("@arangodb/cluster").synchronizeOneShard(
-            params.database, params.shard, params.planId, params.leader);
-        }});
+      try {
+        registerTask({
+          database: jobInfo.database,
+          params: {database: jobInfo.database, shard: jobInfo.shard, 
+                   planId: jobInfo.planId, leader: jobInfo.leader},
+          command: function(params) {
+            require("@arangodb/cluster").synchronizeOneShard(
+              params.database, params.shard, params.planId, params.leader);
+          }});
+      } catch (err) {
+        if (! require("internal").isStopping()) {
+          console.error("Could not registerTask for shard synchronization.");
+        }
+        return;
+      }
       global.KEY_SET("shardSynchronization", "running", jobInfo);
       console.debug("scheduleOneShardSynchronization: have launched job", jobInfo);
       delete jobs.scheduled[shards[0]];
@@ -993,6 +1001,8 @@ function synchronizeOneShard(database, shard, planId, leader) {
   // synchronize this shard from the leader
   // this function will throw if anything goes wrong
 
+  var isStopping = require("internal").isStopping;
+
   var ok = false;
   const rep = require("@arangodb/replication");
 
@@ -1006,6 +1016,9 @@ function synchronizeOneShard(database, shard, planId, leader) {
                         // can only be one syncCollection in flight
                         // at a time
     while (true) {
+      if (isStopping()) {
+        throw "server is shutting down";
+      }
       try {
         sy = rep.syncCollection(shard, 
             { endpoint: ep, incremental: true,
@@ -1087,12 +1100,16 @@ function synchronizeOneShard(database, shard, planId, leader) {
     }
   }
   catch (err2) {
-    console.error("synchronization of local shard '%s/%s' for central '%s/%s' failed: %s",
-                  database, shard, database, planId, JSON.stringify(err2));
+    if (!isStopping()) {
+      console.error("synchronization of local shard '%s/%s' for central '%s/%s' failed: %s",
+                    database, shard, database, planId, JSON.stringify(err2));
+    }
   }
   // Tell others that we are done:
   global.KEY_SET("shardSynchronization", "running", null);
-  launchJob();  // start a new one if needed
+  if (!isStopping()) {
+    launchJob();  // start a new one if needed
+  }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -1726,12 +1743,17 @@ function rebalanceShards() {
         var shardNames = Object.keys(collInfo.shards); 
         for (k = 0; k < shardNames.length; k++) {
           var shardName = shardNames[k];
-          dbTab[collInfo.shards[shardName][0]].push([shardName,true]);
+          shardMap[shardName] = { database: databases[i], collection: collName,
+                                  servers: collInfo.shards[shardName],
+                                  weight: 1 };
+          dbTab[collInfo.shards[shardName][0]].push(
+            { shard: shardName, leader: true,
+              weight: shardMap[shardName].weight });
           for (l = 1; l < collInfo.shards[shardName]; ++l) {
-            dbTab[collInfo.shards[shardName][l]].push([shardName,false]);
+            dbTab[collInfo.shards[shardName][l]].push(
+            { shard: shardName, leader: false,
+              weight: shardMap[shardName].weight });
           }
-          shardMap[shardName] = [databases[i], collName,
-                                 collInfo.shards[shardName]];
         }
       }
     } finally {