diff --git a/src/middlewared/middlewared/plugins/virt/instance.py b/src/middlewared/middlewared/plugins/virt/instance.py
index b64cad6a45be..8aef9b786204 100644
--- a/src/middlewared/middlewared/plugins/virt/instance.py
+++ b/src/middlewared/middlewared/plugins/virt/instance.py
@@ -189,11 +189,14 @@ async def do_create(self, job, data):
 
         devices = {}
         for i in (data['devices'] or []):
-            await self.middleware.call('virt.instance.validate', i, 'virt_instance_create', verrors)
+            await self.middleware.call('virt.instance.validate_device', i, 'virt_instance_create', verrors)
             if i['name'] is None:
                 i['name'] = await self.middleware.call('virt.instance.generate_device_name', devices.keys(), i['dev_type'])
             devices[i['name']] = await self.middleware.call('virt.instance.device_to_incus', data['instance_type'], i)
 
+        if not verrors and data['devices']:
+            await self.middleware.call('virt.instance.validate_devices', data['devices'], 'virt_instance_create', verrors)
+
         verrors.check()
 
         async def running_cb(data):
diff --git a/src/middlewared/middlewared/plugins/virt/instance_device.py b/src/middlewared/middlewared/plugins/virt/instance_device.py
index 9f64bb0c6b87..3c9393b99935 100644
--- a/src/middlewared/middlewared/plugins/virt/instance_device.py
+++ b/src/middlewared/middlewared/plugins/virt/instance_device.py
@@ -242,7 +242,27 @@ async def generate_device_name(self, device_names: list[str], device_type: str)
             i += 1
         return name
 
-    async def __validate_device(self, device, schema, verrors: ValidationErrors, old: dict = None, instance: str = None):
+    @private
+    async def validate_devices(self, devices, schema, verrors: ValidationErrors):
+        unique_src_proxies = []
+        unique_dst_proxies = []
+
+        for device in devices:
+            match device['dev_type']:
+                case 'PROXY':
+                    source = (device['source_proto'], device['source_port'])
+                    if source in unique_src_proxies:
+                        verrors.add(f'{schema}.source_port', 'Source proto/port already in use.')
+                    else:
+                        unique_src_proxies.append(source)
+                    dst = (device['dest_proto'], device['dest_port'])
+                    if dst in unique_dst_proxies:
+                        verrors.add(f'{schema}.dest_port', 'Destination proto/port already in use.')
+                    else:
+                        unique_dst_proxies.append(dst)
+
+    @private
+    async def validate_device(self, device, schema, verrors: ValidationErrors, old: dict = None, instance: str = None):
         match device['dev_type']:
             case 'PROXY':
                 # Skip validation if we are updating and port has not changed
@@ -283,7 +303,7 @@ async def device_add(self, id, device):
             device['name'] = await self.generate_device_name(data['devices'].keys(), device['dev_type'])
 
         verrors = ValidationErrors()
-        await self.__validate_device(device, 'virt_device_add', verrors)
+        await self.validate_device(device, 'virt_device_add', verrors)
         verrors.check()
 
         data['devices'][device['name']] = await self.device_to_incus(instance['type'], device)
@@ -305,7 +325,7 @@ async def device_update(self, id, device):
             raise CallError('Device does not exist.', errno.ENOENT)
 
         verrors = ValidationErrors()
-        await self.__validate_device(device, 'virt_device_update', verrors, old, instance['name'])
+        await self.validate_device(device, 'virt_device_update', verrors, old, instance['name'])
         verrors.check()
 
         data['devices'][device['name']] = await self.device_to_incus(instance['type'], device)