diff --git a/src/Worker/WorkerManager.py b/src/Worker/WorkerManager.py
index 252d34ca..2a71b88e 100644
--- a/src/Worker/WorkerManager.py
+++ b/src/Worker/WorkerManager.py
@@ -20,6 +20,7 @@ class WorkerManager(object):
         self.workers = {}  # Key: ip:port, Value: Worker.Worker
         self.tasks = WorkerTaskManager()
         self.next_task_id = 1
+        self.lock_add_task = gevent.lock.Semaphore(1)
         # {"id": 1, "evt": evt, "workers_num": 0, "site": self.site, "inner_path": inner_path, "done": False, "optional_hash_id": None,
         # "time_started": None, "time_added": time.time(), "peers": peers, "priority": 0, "failed": peer_ids, "lock": None or gevent.lock.RLock}
         self.started_task_num = 0  # Last added task num
@@ -198,7 +199,6 @@ class WorkerManager(object):
         if type(peers) is set:
             peers = list(peers)
 
-
         # Sort by ping
         peers.sort(key=lambda peer: peer.connection.last_ping_delay if peer.connection and peer.connection.last_ping_delay and len(peer.connection.waiting_requests) == 0 and peer.connection.connected else 9999)
 
@@ -463,6 +463,7 @@ class WorkerManager(object):
 
     # Create new task and return asyncresult
     def addTask(self, inner_path, peer=None, priority=0, file_info=None):
+        self.lock_add_task.acquire()
         self.site.onFileStart(inner_path)  # First task, trigger site download started
         task = self.tasks.findTask(inner_path)
         if task:  # Already has task for that file
@@ -476,7 +477,6 @@ class WorkerManager(object):
                 task["failed"].remove(peer)  # New update arrived, remove the peer from failed peers
                 self.log.debug("Removed peer %s from failed %s" % (peer.key, task["inner_path"]))
                 self.startWorkers([peer], reason="Added new task (peer failed before)")
-            return task
         else:  # No task for that file yet
             evt = gevent.event.AsyncResult()
             if peer:
@@ -526,7 +526,8 @@ class WorkerManager(object):
 
             else:
                 self.startWorkers(peers, reason="Added new task")
-            return task
+        self.lock_add_task.release()
+        return task
 
     def addTaskWorker(self, task, worker):
         if task in self.tasks: