diff --git a/lib/prefix.c b/lib/prefix.c
index 219f798dcc..806df0b4c6 100644
--- a/lib/prefix.c
+++ b/lib/prefix.c
@@ -1113,11 +1113,11 @@ in_addr_t ipv4_broadcast_addr(in_addr_t hostaddr, int masklen)
 
 	masklen2ip(masklen, &mask);
 	return (masklen != IPV4_MAX_PREFIXLEN - 1) ?
-						   /* normal case */
-		       (hostaddr | ~mask.s_addr)
-						   :
-						   /* special case for /31 */
-		       (hostaddr ^ ~mask.s_addr);
+		/* normal case */
+		(hostaddr | ~mask.s_addr)
+		   :
+		/* For prefix 31 return 255.255.255.255 (RFC3021) */
+		htonl(0xFFFFFFFF);
 }
 
 /* Utility function to convert ipv4 netmask to prefixes
diff --git a/lib/prefix.h b/lib/prefix.h
index 667627ddfe..fb80c4ca6c 100644
--- a/lib/prefix.h
+++ b/lib/prefix.h
@@ -451,8 +451,7 @@ extern uint8_t ip_masklen(struct in_addr);
 extern void masklen2ip(const int, struct in_addr *);
 /* given the address of a host on a network and the network mask length,
  * calculate the broadcast address for that network;
- * special treatment for /31: returns the address of the other host
- * on the network by flipping the host bit */
+ * special treatment for /31 according to RFC3021 section 3.3 */
 extern in_addr_t ipv4_broadcast_addr(in_addr_t hostaddr, int masklen);
 
 extern int netmask_str2prefix_str(const char *, const char *, char *);