diff --git a/iptables/nft-shared.c b/iptables/nft-shared.c
index 78e4227..f60f5df 100644
--- a/iptables/nft-shared.c
+++ b/iptables/nft-shared.c
@@ -165,7 +165,7 @@ void add_outiface(struct nftnl_rule *r, char *iface, uint32_t op)
 void add_addr(struct nftnl_rule *r, int offset,
 	      void *data, void *mask, size_t len, uint32_t op)
 {
-	const char *m = mask;
+	const unsigned char *m = mask;
 	int i;
 
 	add_payload(r, offset, len, NFT_PAYLOAD_NETWORK_HEADER);