diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
index c5b377ded213..b36b2ebcb22f 100644
--- a/net/ethtool/netlink.c
+++ b/net/ethtool/netlink.c
@@ -305,9 +305,9 @@ static int ethnl_default_doit(struct sk_buff *skb, struct genl_info *info)
 	struct ethnl_req_info *req_info = NULL;
 	const u8 cmd = info->genlhdr->cmd;
 	const struct ethnl_request_ops *ops;
+	int hdr_len, reply_len;
 	struct sk_buff *rskb;
 	void *reply_payload;
-	int reply_len;
 	int ret;
 
 	ops = ethnl_default_requests[cmd];
@@ -336,15 +336,20 @@ static int ethnl_default_doit(struct sk_buff *skb, struct genl_info *info)
 	ret = ops->reply_size(req_info, reply_data);
 	if (ret < 0)
 		goto err_cleanup;
-	reply_len = ret + ethnl_reply_header_size();
+	reply_len = ret;
 	ret = -ENOMEM;
-	rskb = ethnl_reply_init(reply_len, req_info->dev, ops->reply_cmd,
+	rskb = ethnl_reply_init(reply_len + ethnl_reply_header_size(),
+				req_info->dev, ops->reply_cmd,
 				ops->hdr_attr, info, &reply_payload);
 	if (!rskb)
 		goto err_cleanup;
+	hdr_len = rskb->len;
 	ret = ops->fill_reply(rskb, req_info, reply_data);
 	if (ret < 0)
 		goto err_msg;
+	WARN_ONCE(rskb->len - hdr_len > reply_len,
+		  "ethnl cmd %d: calculated reply length %d, but consumed %d\n",
+		  cmd, reply_len, rskb->len - hdr_len);
 	if (ops->cleanup_data)
 		ops->cleanup_data(reply_data);