diff --git a/metagpt/utils/token_counter.py b/metagpt/utils/token_counter.py
index 591bb60f0..a5a65803a 100644
--- a/metagpt/utils/token_counter.py
+++ b/metagpt/utils/token_counter.py
@@ -96,7 +96,7 @@ def count_string_tokens(string: str, model_name: str) -> int:
     return len(encoding.encode(string))
 
 
-def get_max_completion_tokens(messages: list[dict], model: str, default: int) -> int: 
+def get_max_completion_tokens(messages: list[dict], model: str, default: int) -> int:
     """Calculate the maximum number of completion tokens for a given model and list of messages.
 
     Args:
@@ -108,4 +108,4 @@ def get_max_completion_tokens(messages: list[dict], model: str, default: int) ->
     """
     if model not in TOKEN_MAX:
         return default
-    return TOKEN_MAX[model] - count_message_tokens(messages)
+    return TOKEN_MAX[model] - count_message_tokens(messages) - 1