diff --git a/gns3server/compute/dynamips/nodes/router.py b/gns3server/compute/dynamips/nodes/router.py
index 7b638018..7b0e4731 100644
--- a/gns3server/compute/dynamips/nodes/router.py
+++ b/gns3server/compute/dynamips/nodes/router.py
@@ -380,6 +380,7 @@ class Router(BaseNode):
                 except OSError as e:
                     log.warn("Could not delete file {}: {}".format(file, e))
                     continue
+        self.manager.release_dynamips_id(self.project.id, self.dynamips_id)
 
     @property
     def platform(self):
diff --git a/gns3server/controller/project.py b/gns3server/controller/project.py
index f4913d1b..db3b2d79 100644
--- a/gns3server/controller/project.py
+++ b/gns3server/controller/project.py
@@ -584,10 +584,10 @@ class Project:
         """
         Delete the project on computes but not on controller
         """
-        for compute in self._project_created_on_compute:
+        for compute in list(self._project_created_on_compute):
             if compute.id != "local":
                 yield from compute.delete("/projects/{}".format(self._id))
-        self._project_created_on_compute = set()
+                self._project_created_on_compute.remove(compute)
 
     @classmethod
     def _get_default_project_directory(cls):