diff --git a/net/ethtool/cabletest.c b/net/ethtool/cabletest.c
index d365ad5f5434..f25da884b3dd 100644
--- a/net/ethtool/cabletest.c
+++ b/net/ethtool/cabletest.c
@@ -346,7 +346,7 @@ int ethnl_act_cable_test_tdr(struct sk_buff *skb, struct genl_info *info)
 	phydev = ethnl_req_get_phydev(&req_info,
 				      tb[ETHTOOL_A_CABLE_TEST_TDR_HEADER],
 				      info->extack);
-	if (!IS_ERR_OR_NULL(phydev)) {
+	if (IS_ERR_OR_NULL(phydev)) {
 		ret = -EOPNOTSUPP;
 		goto out_dev_put;
 	}