diff --git a/ipcalc.c b/ipcalc.c

index f2bc47a..04c9372 100644

--- a/ipcalc.c

+++ b/ipcalc.c

@@ -146,7 +146,12 @@ static struct in_addr calc_broadcast(struct in_addr addr, int prefix)

 	mask.s_addr = prefix2mask(prefix);

 	memset(&broadcast, 0, sizeof(broadcast));

-	broadcast.s_addr = (addr.s_addr & mask.s_addr) | ~mask.s_addr;

+

+	/* if prefix is set to 31 return 255.255.255.255 (RFC3021) */

+	if (mask.s_addr ==  htonl(0xFFFFFFFE))

+		broadcast.s_addr = htonl(0xFFFFFFFF);

+	else

+		broadcast.s_addr = (addr.s_addr & mask.s_addr) | ~mask.s_addr;

 	return broadcast;

 }

diff --git a/tests/192.168.1.5-31 b/tests/192.168.1.5-31

index fee8227..b720b56 100644

--- a/tests/192.168.1.5-31

+++ b/tests/192.168.1.5-31

@@ -1,4 +1,4 @@

 NETMASK=255.255.255.254

 PREFIX=31

-BROADCAST=192.168.1.5

+BROADCAST=255.255.255.255

 NETWORK=192.168.1.4