diff --git a/gns3server/modules/dynamips/nodes/atm_switch.py b/gns3server/modules/dynamips/nodes/atm_switch.py
index bf56945b..0fb9e1e1 100644
--- a/gns3server/modules/dynamips/nodes/atm_switch.py
+++ b/gns3server/modules/dynamips/nodes/atm_switch.py
@@ -116,7 +116,8 @@ class ATMSwitch(Device):
             log.info('ATM switch "{name}" [{id}] has been deleted'.format(name=self._name, id=self._id))
         except DynamipsError:
             log.debug("Could not properly delete ATM switch {}".format(self._name))
-        self._hypervisor.devices.remove(self)
+        if self._hypervisor and self in self._hypervisor.devices:
+            self._hypervisor.devices.remove(self)
         if self._hypervisor and not self._hypervisor.devices:
             yield from self.hypervisor.stop()
 
diff --git a/gns3server/modules/dynamips/nodes/bridge.py b/gns3server/modules/dynamips/nodes/bridge.py
index 174fbb86..7dc4e31b 100644
--- a/gns3server/modules/dynamips/nodes/bridge.py
+++ b/gns3server/modules/dynamips/nodes/bridge.py
@@ -80,8 +80,10 @@ class Bridge(Device):
         Deletes this bridge.
         """
 
-        self._hypervisor.devices.remove(self)
-        yield from self._hypervisor.send('nio_bridge delete "{}"'.format(self._name))
+        if self._hypervisor and self in self._hypervisor.devices:
+            self._hypervisor.devices.remove(self)
+        if self._hypervisor and not self._hypervisor.devices:
+            yield from self._hypervisor.send('nio_bridge delete "{}"'.format(self._name))
 
     @asyncio.coroutine
     def add_nio(self, nio):
diff --git a/gns3server/modules/dynamips/nodes/ethernet_hub.py b/gns3server/modules/dynamips/nodes/ethernet_hub.py
index 23fb2129..d41e5117 100644
--- a/gns3server/modules/dynamips/nodes/ethernet_hub.py
+++ b/gns3server/modules/dynamips/nodes/ethernet_hub.py
@@ -74,7 +74,7 @@ class EthernetHub(Bridge):
         Deletes this hub.
         """
 
-        for nio in self._nios.values():
+        for nio in self._nios:
             if nio and isinstance(nio, NIOUDP):
                 self.manager.port_manager.release_udp_port(nio.lport)
 
diff --git a/gns3server/modules/dynamips/nodes/ethernet_switch.py b/gns3server/modules/dynamips/nodes/ethernet_switch.py
index 3814e720..a748a9b3 100644
--- a/gns3server/modules/dynamips/nodes/ethernet_switch.py
+++ b/gns3server/modules/dynamips/nodes/ethernet_switch.py
@@ -124,7 +124,8 @@ class EthernetSwitch(Device):
             log.info('Ethernet switch "{name}" [{id}] has been deleted'.format(name=self._name, id=self._id))
         except DynamipsError:
             log.debug("Could not properly delete Ethernet switch {}".format(self._name))
-        self._hypervisor.devices.remove(self)
+        if self._hypervisor and self in self._hypervisor.devices:
+            self._hypervisor.devices.remove(self)
         if self._hypervisor and not self._hypervisor.devices:
             yield from self.hypervisor.stop()
 
diff --git a/gns3server/modules/dynamips/nodes/frame_relay_switch.py b/gns3server/modules/dynamips/nodes/frame_relay_switch.py
index 1a21dd56..b46055b4 100644
--- a/gns3server/modules/dynamips/nodes/frame_relay_switch.py
+++ b/gns3server/modules/dynamips/nodes/frame_relay_switch.py
@@ -115,7 +115,8 @@ class FrameRelaySwitch(Device):
             log.info('Frame Relay switch "{name}" [{id}] has been deleted'.format(name=self._name, id=self._id))
         except DynamipsError:
             log.debug("Could not properly delete Frame relay switch {}".format(self._name))
-        self._hypervisor.devices.remove(self)
+        if self._hypervisor and self in self._hypervisor.devices:
+            self._hypervisor.devices.remove(self)
         if self._hypervisor and not self._hypervisor.devices:
             yield from self.hypervisor.stop()