diff --git a/include/uapi/linux/xfrm.h b/include/uapi/linux/xfrm.h
index ffc6a5391bb7bb8f7543cb36fb16487596fd3255..66073c082a06004f0387cce30bd85b4d2ddbaf65 100644
--- a/include/uapi/linux/xfrm.h
+++ b/include/uapi/linux/xfrm.h
@@ -505,6 +505,12 @@ struct xfrm_user_offload {
 	int				ifindex;
 	__u8				flags;
 };
+/* This flag was exposed without any kernel code that supporting it.
+ * Unfortunately, strongswan has the code that uses sets this flag,
+ * which makes impossible to reuse this bit.
+ *
+ * So leave it here to make sure that it won't be reused by mistake.
+ */
 #define XFRM_OFFLOAD_IPV6	1
 #define XFRM_OFFLOAD_INBOUND	2
 
diff --git a/net/xfrm/xfrm_device.c b/net/xfrm/xfrm_device.c
index e843b0d9e2a61c16551be51f69bc441ccad4f921..c255aac6b816b4911b435ae76cd3377b88f2d9dd 100644
--- a/net/xfrm/xfrm_device.c
+++ b/net/xfrm/xfrm_device.c
@@ -223,6 +223,9 @@ int xfrm_dev_state_add(struct net *net, struct xfrm_state *x,
 	if (x->encap || x->tfcpad)
 		return -EINVAL;
 
+	if (xuo->flags & ~(XFRM_OFFLOAD_IPV6 | XFRM_OFFLOAD_INBOUND))
+		return -EINVAL;
+
 	dev = dev_get_by_index(net, xuo->ifindex);
 	if (!dev) {
 		if (!(xuo->flags & XFRM_OFFLOAD_INBOUND)) {
@@ -261,7 +264,8 @@ int xfrm_dev_state_add(struct net *net, struct xfrm_state *x,
 	xso->dev = dev;
 	xso->real_dev = dev;
 	xso->num_exthdrs = 1;
-	xso->flags = xuo->flags;
+	/* Don't forward bit that is not implemented */
+	xso->flags = xuo->flags & ~XFRM_OFFLOAD_IPV6;
 
 	err = dev->xfrmdev_ops->xdo_dev_state_add(x);
 	if (err) {