diff --git a/src/fastmcp/client/sampling/handlers/openai.py b/src/fastmcp/client/sampling/handlers/openai.py
index 362e05905..38f5ff356 100644
--- a/src/fastmcp/client/sampling/handlers/openai.py
+++ b/src/fastmcp/client/sampling/handlers/openai.py
@@ -84,8 +84,9 @@ class OpenAISamplingHandler:
         kwargs: dict[str, Any] = {
             "model": model,
             "messages": openai_messages,
-            "max_completion_tokens": params.maxTokens,
         }
+        if params.maxTokens is not None:
+            kwargs["max_completion_tokens"] = params.maxTokens
         if params.temperature is not None:
             kwargs["temperature"] = params.temperature
         if params.stopSequences: