diff --git a/src/scheduler.js b/src/scheduler.js
index b27a4300e..b8e4904f4 100644
--- a/src/scheduler.js
+++ b/src/scheduler.js
@@ -30,29 +30,40 @@ function sync(callback) {
         // stop tasks of apps that went away
         var allAppIds = allApps.map(function (app) { return app.id; });
         var removedAppIds = _.difference(Object.keys(gTasks), allAppIds);
-        removedAppIds.forEach(stopJobs);
+        async.eachSeries(removedAppIds, stopJobs, function (error) {
+            if (error) debug('Error stopping jobs : %j', error);
 
-        // start tasks of new apps
-        allApps.forEach(function (app) { resetTasks(app.id, app.manifest.addons.scheduler || null); });
+            // start tasks of new apps
+            allApps.forEach(function (app) {
+                resetTasks(app.id, app.manifest.addons.scheduler || null);
+            });
+
+            debug('Done syncing');
+        });
     });
 }
 
-function stopJobs(appId) {
+function stopJobs(appId, callback) {
     assert.strictEqual(typeof appId, 'string');
 
     debug('stopJobs for %s', appId);
 
-    for (var job in gTasks[appId].jobs) {
-        job.cronJob.stop();
-    }
+    async.eachSeries(Object.keys(gTasks[appId].jobs), function (taskName, iteratorDone) {
+        gTasks[appId].jobs[taskName].cronJob.stop();
+        killTask(appId, taskName, iteratorDone);
+    }, function (error) {
+        if (error) return callback(error);
 
-    delete gTasks[appId];
+        delete gTasks[appId];
+
+        callback();
+    });
 }
 
-function startJobs(appId, tasksConfig) {
+function createCronJobs(appId, tasksConfig) {
     gTasks[appId] = { tasksConfig: tasksConfig, jobs: { } };
 
-    debug('startJobs for %s', appId);
+    debug('creating cron jobs for %s', appId);
 
     Object.keys(tasksConfig).forEach(function (taskName) {
         var task = tasksConfig[taskName];
@@ -61,7 +72,7 @@ function startJobs(appId, tasksConfig) {
 
         var job = new CronJob({
             cronTime: '00 ' + task.schedule, // at this point, the pattern has been validated
-            onTick: runTask.bind(null, appId, taskName, task),
+            onTick: doTask.bind(null, appId, taskName, task),
             start: true
         });
 
@@ -71,21 +82,32 @@ function startJobs(appId, tasksConfig) {
 
 function resetTasks(appId, tasksConfig) {
     assert.strictEqual(typeof appId, 'string');
-    assert.strictEqual(typeof tasksConfig, 'object');
+    assert.strictEqual(typeof tasksConfig, 'object'); // can be null
 
     // cleanup existing state
     if (appId in gTasks) {
         if (_.isEqual(gTasks[appId].tasksConfig, tasksConfig)) return; // nothing changed
 
-        stopJobs(appId);
+        stopJobs(appId); // something changes, stop all the existing jobs
     }
 
     if (!tasksConfig) return;
 
-    startJobs(appId, tasksConfig);
+    createCronJobs(appId, tasksConfig);
 }
 
-function runTask(appId, taskName, task, callback) {
+function killTask(appId, taskName, callback) {
+    var containerId = gTasks[appId].jobs[taskName].containerId;
+
+    if (!containerId) return callback();
+
+    async.series([
+        docker.stopContainer.bind(null, containerId),
+        docker.deleteContainer.bind(null, containerId)
+    ], callback);
+}
+
+function doTask(appId, taskName, task, callback) {
     assert.strictEqual(typeof appId, 'string');
     assert.strictEqual(typeof taskName, 'string');
     assert.strictEqual(typeof task, 'object');
@@ -96,12 +118,8 @@ function runTask(appId, taskName, task, callback) {
     var containerId = gTasks[appId].jobs[taskName].containerId;
 
     if (containerId) {
-        debug('task %s/%s is already running');
-        async.series([
-            docker.stopContainer.bind(null, containerId),
-            docker.deleteContainer.bind(null, containerId)
-        ], callback);
-        return;
+        debug('task %s/%s is already running. killing it');
+        return killTask(appId, taskName, callback);
     }
 
     apps.get(appId, function (error, app) {