diff --git a/netbox_agent/network.py b/netbox_agent/network.py
index bb1d1610..7ceb7173 100644
--- a/netbox_agent/network.py
+++ b/netbox_agent/network.py
@@ -337,10 +337,11 @@ def _update_interface_macs_legacy(self, nic, macs):
                 )
 
     def _update_interface_macs_new(self, nic, macs):
-        if hasattr(self.nb_net, 'virtual_machines'):
-            object_type = 'virtualization.vminterface'
-        else:
-            object_type = 'dcim.interface'
+        object_type = (
+            "virtualization.vminterface"
+            if self.assigned_object_type == "virtualization.vminterface"
+            else "dcim.interface"
+        )
         try:
             nb_macs = list(self.nb.dcim.mac_addresses.filter(
                 assigned_object_type=object_type,
@@ -546,6 +547,7 @@ def create_or_update_netbox_network_cards(self):
         if config.update_all is None or config.update_network is None:
             return None
         logging.debug("Creating/Updating NIC...")
+        is_netbox_42_plus = version.parse(nb.version) >= version.parse("4.2")
 
         # delete unknown interface
         nb_nics = list(self.get_netbox_network_cards())
@@ -602,12 +604,6 @@ def batched(it, n):
                 interface.name = nic['name']
                 nic_update += 1
             
-            if nic['mac'] != interface.mac_address:
-                logging.info('Updating interface {interface} mac_address to: {mac}'.format(
-                    interface=interface, mac=nic['mac']))
-                interface.mac_address = nic['mac']
-                nic_update += 1
-            
             ret, interface = self.reset_vlan_on_interface(nic, interface)
             nic_update += ret
 
@@ -620,21 +616,18 @@ def batched(it, n):
                 interface.name = nic["name"]
                 nic_update += 1
 
-            if version.parse(nb.version) >= version.parse("4.2"):
-                # Create MAC objects
+            if is_netbox_42_plus:
                 if nic["mac"]:
                     self.update_interface_macs(interface, [nic["mac"]])
-
-            if nic["mac"] and nic["mac"] != interface.mac_address:
+                    # Refresh interface so future saves don't include stale primary MAC diffs
+                    interface = self.nb_net.interfaces.get(id=interface.id)
+            elif nic["mac"] and nic["mac"] != interface.mac_address:
                 logging.info(
-                    "Updating interface {interface} mac to: {mac}".format(
+                    "Updating interface {interface} mac_address to: {mac}".format(
                         interface=interface, mac=nic["mac"]
                     )
                 )
-                if version.parse(nb.version) < version.parse("4.2"):
-                    interface.mac_address = nic["mac"]
-                else:
-                    interface.primary_mac_address = {"mac_address": nic["mac"]}
+                interface.mac_address = nic["mac"]
                 nic_update += 1
 
             if hasattr(interface, "mtu"):
@@ -691,6 +684,15 @@ def batched(it, n):
                 # sync local IPs
                 for ip in nic["ip"]:
                     self.create_or_update_netbox_ip_on_interface(ip, interface)
+
+            if is_netbox_42_plus:
+                primary_obj = getattr(interface, "primary_mac_address", None)
+                if primary_obj and not isinstance(primary_obj, int):
+                    primary_id = getattr(primary_obj, "id", None)
+                    if primary_id is None and isinstance(primary_obj, dict):
+                        primary_id = primary_obj.get("id")
+                    if primary_id:
+                        interface.primary_mac_address = primary_id
             if nic_update > 0:
                 interface.save()