diff --git a/netbox/dcim/api/serializers.py b/netbox/dcim/api/serializers.py
index ef26e4ae8..e041d4c02 100644
--- a/netbox/dcim/api/serializers.py
+++ b/netbox/dcim/api/serializers.py
@@ -897,6 +897,7 @@ class InterfaceSerializer(NetBoxModelSerializer, CabledObjectSerializer, Connect
         ]
 
     def validate(self, data):
+
         # Validate many-to-many VLAN assignments
         device = self.instance.device if self.instance else data.get('device')
         for vlan in data.get('tagged_vlans', []):
diff --git a/netbox/dcim/models/device_component_templates.py b/netbox/dcim/models/device_component_templates.py
index 3b136987d..20f99ecb2 100644
--- a/netbox/dcim/models/device_component_templates.py
+++ b/netbox/dcim/models/device_component_templates.py
@@ -120,6 +120,10 @@ class ModularComponentTemplateModel(ComponentTemplateModel):
             ),
         )
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.__original_device_type = self.device_type_id
+
     def to_objectchange(self, action):
         objectchange = super().to_objectchange(action)
         if self.device_type is not None:
@@ -131,6 +135,11 @@ class ModularComponentTemplateModel(ComponentTemplateModel):
     def clean(self):
         super().clean()
 
+        if self.pk is not None and self.__original_device_type != self.device_type_id:
+            raise ValidationError({
+                "device": "device_type field is read-only and not updatable."
+            })
+
         # A component template must belong to a DeviceType *or* to a ModuleType
         if self.device_type and self.module_type:
             raise ValidationError(
diff --git a/netbox/dcim/models/device_components.py b/netbox/dcim/models/device_components.py
index 992f88560..5b0442dff 100644
--- a/netbox/dcim/models/device_components.py
+++ b/netbox/dcim/models/device_components.py
@@ -80,7 +80,7 @@ class ComponentModel(NetBoxModel):
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
-        self.__original_device = self.device
+        self.__original_device = self.device_id
 
     def __str__(self):
         if self.label:
@@ -95,7 +95,7 @@ class ComponentModel(NetBoxModel):
     def clean(self):
         super().clean()
 
-        if self.pk is None and self.__original_device != self.device:
+        if self.pk is not None and self.__original_device != self.device_id:
             raise ValidationError({
                 "device": "Device field is read-only and not updatable."
             })