diff --git a/netbox/dcim/api/serializers_/device_components.py b/netbox/dcim/api/serializers_/device_components.py
index 16b68671b..468c7b496 100644
--- a/netbox/dcim/api/serializers_/device_components.py
+++ b/netbox/dcim/api/serializers_/device_components.py
@@ -243,22 +243,22 @@ class InterfaceSerializer(NetBoxModelSerializer, CabledObjectSerializer, Connect
             mode = None
             tagged_vlans = []
 
-            if self.instance.pk and 'mode' in data.keys():
-                mode = data.get('mode') if 'mode' in data.keys() else self.instance.get('mode')
-            elif 'mode' in data.keys():
-                mode = data.get('mode')
-
-            if self.instance.pk and 'tagged_vlans' in data.keys():
-                tagged_vlans = data.get('tagged_vlans') if 'tagged_vlans' in data.keys() else \
-                    self.instance.tagged_vlans.all()
-            elif 'tagged_vlans' in data.keys():
-                tagged_vlans = data.get('tagged_vlans')
-
-            if self.instance.pk and 'untagged_vlan' in data.keys():
-                untagged_vlan = data.get('untagged_vlan') if 'untagged_vlan' in data.keys() else \
-                    self.instance.untagged_vlan
-            elif 'untagged_vlan' in data.keys():
-                untagged_vlan = data.get('untagged_vlan')
+            if self.instance:
+                if 'mode' in data.keys():
+                    mode = data.get('mode') if 'mode' in data.keys() else self.instance.get('mode')
+                if 'tagged_vlans' in data.keys():
+                    tagged_vlans = data.get('tagged_vlans') if 'tagged_vlans' in data.keys() else \
+                        self.instance.tagged_vlans.all()
+                if 'untagged_vlan' in data.keys():
+                    untagged_vlan = data.get('untagged_vlan') if 'untagged_vlan' in data.keys() else \
+                        self.instance.untagged_vlan
+            else:
+                if 'mode' in data.keys():
+                    mode = data.get('mode')
+                if 'tagged_vlans' in data.keys():
+                    tagged_vlans = data.get('tagged_vlans')
+                if 'untagged_vlan' in data.keys():
+                    untagged_vlan = data.get('untagged_vlan')
 
             if mode != InterfaceModeChoices.MODE_TAGGED and tagged_vlans:
                 raise serializers.ValidationError({
diff --git a/netbox/dcim/forms/model_forms.py b/netbox/dcim/forms/model_forms.py
index b26247a94..95908bd41 100644
--- a/netbox/dcim/forms/model_forms.py
+++ b/netbox/dcim/forms/model_forms.py
@@ -1368,22 +1368,23 @@ class InterfaceForm(InterfaceCommonForm, ModularDeviceComponentForm):
         tagged_vlans = []
         untagged_vlan = None
 
-        if self.instance.pk and 'mode' in self.cleaned_data.keys():
-            mode = self.cleaned_data.get('mode') if 'mode' in self.cleaned_data.keys() else self.instance.get('mode')
-        elif 'mode' in self.cleaned_data.keys():
-            mode = self.cleaned_data.get('mode')
-
-        if self.instance.pk and 'tagged_vlans' in self.cleaned_data.keys():
-            tagged_vlans = self.cleaned_data.get('tagged_vlans') if 'tagged_vlans' in self.cleaned_data.keys() else\
-                self.instance.tagged_vlans.all()
-        elif 'tagged_vlans' in self.cleaned_data.keys():
-            tagged_vlans = self.cleaned_data.get('tagged_vlans')
-
-        if self.instance.pk and 'untagged_vlan' in self.cleaned_data.keys():
-            untagged_vlan = self.cleaned_data.get('untagged_vlan') if 'untagged_vlan' in self.cleaned_data.keys() else\
-                self.instance.untagged_vlan
-        elif 'untagged_vlan' in self.cleaned_data.keys():
-            untagged_vlan = self.cleaned_data.get('untagged_vlan')
+        if self.instance:
+            if 'mode' in self.cleaned_data.keys():
+                mode = self.cleaned_data.get('mode') if 'mode' in self.cleaned_data.keys() else\
+                    self.instance.get('mode')
+            if 'tagged_vlans' in self.cleaned_data.keys():
+                tagged_vlans = self.cleaned_data.get('tagged_vlans') if 'tagged_vlans' in self.cleaned_data.keys() else\
+                    self.instance.tagged_vlans.all()
+            if 'untagged_vlan' in self.cleaned_data.keys():
+                untagged_vlan = self.cleaned_data.get('untagged_vlan') if 'untagged_vlan' in self.cleaned_data.keys()\
+                    else self.instance.untagged_vlan
+        else:
+            if 'mode' in self.cleaned_data.keys():
+                mode = self.cleaned_data.get('mode')
+            if 'tagged_vlans' in self.cleaned_data.keys():
+                tagged_vlans = self.cleaned_data.get('tagged_vlans')
+            if 'untagged_vlan' in self.cleaned_data.keys():
+                untagged_vlan = self.cleaned_data.get('untagged_vlan')
 
         if mode != InterfaceModeChoices.MODE_TAGGED and tagged_vlans:
             raise forms.ValidationError({