diff --git a/nbxsync/utils/sync/hostsync.py b/nbxsync/utils/sync/hostsync.py
index b9efbdfe..2e307d7a 100644
--- a/nbxsync/utils/sync/hostsync.py
+++ b/nbxsync/utils/sync/hostsync.py
@@ -553,6 +553,29 @@ def check_default_hostinterface(self):
                         continue
                     desired_hostinterfaces.append(params)
 
+                # host.update() treats 'interfaces' as the complete, authoritative list: any
+                # interface on the host that is missing from it gets DELETED, and an interface
+                # that still carries items cannot be deleted - Zabbix then rejects the whole
+                # call with 'Invalid params. Interface is linked to item "..." on "..."'.
+                # Carry interfaces unknown to NetBox along untouched; pruning stale ones is
+                # verify_hostinterfaces()'s job, not this one.
+                known_interfaceids = {str(int(params['interfaceid'])) for params in desired_hostinterfaces}
+                netbox_default_types = {int(params['type']) for params in desired_hostinterfaces if int(params.get('main', 0)) == 1}
+
+                for zabbix_hostinterface in zabbix_hostinterfaces:
+                    if str(int(zabbix_hostinterface['interfaceid'])) in known_interfaceids:
+                        continue
+
+                    carried = {key: zabbix_hostinterface[key] for key in ('interfaceid', 'type', 'ip', 'dns', 'port', 'useip') if key in zabbix_hostinterface}
+                    if zabbix_hostinterface.get('details'):
+                        carried['details'] = zabbix_hostinterface['details']
+
+                    # Only one interface per type may be main. Where NetBox supplies the
+                    # default for a type, every other interface of that type has to yield;
+                    # types NetBox knows nothing about keep whatever Zabbix already had.
+                    carried['main'] = 0 if int(zabbix_hostinterface['type']) in netbox_default_types else int(zabbix_hostinterface.get('main', 0))
+                    desired_hostinterfaces.append(carried)
+
                 self.api.host.update(hostid=hostid, interfaces=desired_hostinterfaces)
         return