diff --git a/lmdeploy/tokenizer.py b/lmdeploy/tokenizer.py
index e977005588..fb4364602a 100644
--- a/lmdeploy/tokenizer.py
+++ b/lmdeploy/tokenizer.py
@@ -624,7 +624,14 @@ def encode(self,
         Returns:
             list[int]: token ids
         """
-        return self.model.encode(s, add_bos, add_special_tokens, **kwargs)
+        encoded = self.model.encode(s, add_bos, add_special_tokens, **kwargs)
+        if encoded[:2] == [self.bos_token_id] * 2:
+            get_logger('lmdeploy').warn(
+                f'Detected duplicate bos token {self.bos_token_id} in prompt, '
+                'this will likely reduce response quality, one of them will be'
+                'removed')
+            encoded = encoded[1:]
+        return encoded
 
     def decode(
         self,