diff --git a/whisper_live/server.py b/whisper_live/server.py
index 5815d20..749ed78 100644
--- a/whisper_live/server.py
+++ b/whisper_live/server.py
@@ -5,7 +5,7 @@ import json
 import functools
 import logging
 from enum import Enum
-from typing import List
+from typing import List, Optional
 
 import torch
 import numpy as np
@@ -156,6 +156,8 @@ class TranscriptionServer:
         self, websocket, options, faster_whisper_custom_model_path,
         whisper_tensorrt_path, trt_multilingual
     ):
+        client: Optional[ServeClientBase] = None
+
         if self.backend == "tensorrt":
             try:
                 client = ServeClientTensorRT(
@@ -196,6 +198,9 @@ class TranscriptionServer:
             )
             logging.info("Running faster_whisper backend.")
 
+        if client is None:
+            raise ValueError(f"Backend type {self.backend} not recognised or not handled.")
+
         self.client_manager.add_client(websocket, client)
 
     def get_audio_from_websocket(self, websocket):