diff --git a/include/uapi/linux/ipv6_route.h b/include/uapi/linux/ipv6_route.h
index f6598d1c886e..316e838b7470 100644
--- a/include/uapi/linux/ipv6_route.h
+++ b/include/uapi/linux/ipv6_route.h
@@ -34,7 +34,7 @@
 #define RTF_PREF(pref)	((pref) << 27)
 #define RTF_PREF_MASK	0x18000000
 
-#define RTF_PCPU	0x40000000
+#define RTF_PCPU	0x40000000	/* read-only: can not be set by user */
 #define RTF_LOCAL	0x80000000
 
 
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 9f0aa255e288..6c91d5c4a92c 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1758,6 +1758,10 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg)
 	int addr_type;
 	int err = -EINVAL;
 
+	/* RTF_PCPU is an internal flag; can not be set by userspace */
+	if (cfg->fc_flags & RTF_PCPU)
+		goto out;
+
 	if (cfg->fc_dst_len > 128 || cfg->fc_src_len > 128)
 		goto out;
 #ifndef CONFIG_IPV6_SUBTREES