diff --git a/voltha/core/device_agent.py b/voltha/core/device_agent.py
index 2eca638..25eda22 100644
--- a/voltha/core/device_agent.py
+++ b/voltha/core/device_agent.py
@@ -374,7 +374,13 @@
             self.log.debug('disable-device', device=device, dry_run=dry_run)
             if not dry_run:
                 # Remove all flows before disabling device
-                # self._delete_all_flows()
+                # Only do this for ONUs. ponsim seems to want the flows
+                # to be removed on onu disable and it does not seem to
+                # hurt the real devices. Flows on OLT are not removed when
+                # OLT is disabled - each adapter may do its own thing
+                # for disable -e.g. OpenOLT disables the NNI interface.
+                if not device.root:
+                    self._delete_all_flows()
                 yield self.adapter_agent.disable_device(device)
         except Exception, e:
             self.log.exception('error', e=e)