diff --git a/gns3server/modules/iou/__init__.py b/gns3server/modules/iou/__init__.py
index 3cdddfe7..7b80107a 100644
--- a/gns3server/modules/iou/__init__.py
+++ b/gns3server/modules/iou/__init__.py
@@ -49,9 +49,10 @@ class IOU(BaseManager):
     def close_vm(self, vm_id, *args, **kwargs):
 
         vm = self.get_vm(vm_id)
-        i = self._used_application_ids[vm_id]
-        self._free_application_ids.insert(0, i)
-        del self._used_application_ids[vm_id]
+        if vm_id in self._used_application_ids:
+            i = self._used_application_ids[vm_id]
+            self._free_application_ids.insert(0, i)
+            del self._used_application_ids[vm_id]
         yield from super().close_vm(vm_id, *args, **kwargs)
         return vm