diff --git a/gns3server/modules/base_manager.py b/gns3server/modules/base_manager.py
index 5c8488f7..7aec4a13 100644
--- a/gns3server/modules/base_manager.py
+++ b/gns3server/modules/base_manager.py
@@ -44,10 +44,11 @@ class BaseManager:
     Responsible of management of a VM pool
     """
 
-    _convert_lock = asyncio.Lock()
+    _convert_lock = None
 
     def __init__(self):
 
+        BaseManager._convert_lock = asyncio.Lock()
         self._vms = {}
         self._port_manager = None
         self._config = Config.instance()
diff --git a/gns3server/modules/dynamips/__init__.py b/gns3server/modules/dynamips/__init__.py
index 23af464b..0b19c0be 100644
--- a/gns3server/modules/dynamips/__init__.py
+++ b/gns3server/modules/dynamips/__init__.py
@@ -105,11 +105,12 @@ class Dynamips(BaseManager):
 
     _VM_CLASS = DynamipsVM
     _DEVICE_CLASS = DynamipsDevice
-    _ghost_ios_lock = asyncio.Lock()
+    _ghost_ios_lock = None
 
     def __init__(self):
 
         super().__init__()
+        Dynamips._ghost_ios_lock = asyncio.Lock()
         self._devices = {}
         self._ghost_files = set()
         self._dynamips_path = None