diff --git a/net/ipv6/netfilter/ip6t_NPT.c b/net/ipv6/netfilter/ip6t_NPT.c
index 33608c610276..cb631143721c 100644
--- a/net/ipv6/netfilter/ip6t_NPT.c
+++ b/net/ipv6/netfilter/ip6t_NPT.c
@@ -57,7 +57,7 @@ static bool ip6t_npt_map_pfx(const struct ip6t_npt_tginfo *npt,
 		if (pfx_len - i >= 32)
 			mask = 0;
 		else
-			mask = htonl(~((1 << (pfx_len - i)) - 1));
+			mask = htonl((1 << (i - pfx_len + 32)) - 1);
 
 		idx = i / 32;
 		addr->s6_addr32[idx] &= mask;