diff --git a/routstr/proxy.py b/routstr/proxy.py
index 89660837..38b8fc45 100644
--- a/routstr/proxy.py
+++ b/routstr/proxy.py
@@ -636,6 +636,12 @@ async def proxy(
     if request_body:
         try:
             request_body_dict = json.loads(request_body)
+
+            if "max_tokens" in request_body_dict:
+                raise HTTPException(
+                    status_code=400,
+                    detail={"error": "max_tokens must be an integer (without quotes)"},
+                )
             logger.debug(
                 "Request body parsed",
                 extra={