diff --git a/gns3server/controller/drawing.py b/gns3server/controller/drawing.py
index 4ef324b4..de929b2f 100644
--- a/gns3server/controller/drawing.py
+++ b/gns3server/controller/drawing.py
@@ -16,7 +16,6 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import hashlib
-import asyncio
 import base64
 import uuid
 import re
diff --git a/gns3server/controller/project.py b/gns3server/controller/project.py
index 04d4a798..29ab0842 100644
--- a/gns3server/controller/project.py
+++ b/gns3server/controller/project.py
@@ -684,6 +684,8 @@ class Project:
     @open_required
     async def delete_drawing(self, drawing_id):
         drawing = self.get_drawing(drawing_id)
+        if drawing.locked:
+            raise aiohttp.web.HTTPConflict(text="Drawing ID {} cannot be deleted because it is locked".format(drawing_id))
         del self._drawings[drawing.id]
         self.dump()
         self.emit_notification("drawing.deleted", drawing.__json__())