diff --git a/ChangeLog b/ChangeLog
index 83ee634a17..4a5f136531 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+1999-05-30  Ulrich Drepper  <drepper@cygnus.com>
+
+	* inet/netinet/in.h: Mark ntoh* and hton* as constant functions.
+
 1999-05-30  Andreas Jaeger  <aj@arthur.rhein-neckar.de>
 
 	* manual/stdio.texi: Fix some typos.
diff --git a/inet/netinet/in.h b/inet/netinet/in.h
index ee49fd0428..fc8f169bcf 100644
--- a/inet/netinet/in.h
+++ b/inet/netinet/in.h
@@ -230,10 +230,10 @@ struct ipv6_mreq
    this was a short-sighted decision since on different systems the types
    may have different representations but the values are always the same.  */
 
-extern uint32_t ntohl __P ((uint32_t __netlong));
-extern uint16_t ntohs __P ((uint16_t __netshort));
-extern uint32_t htonl __P ((uint32_t __hostlong));
-extern uint16_t htons __P ((uint16_t __hostshort));
+extern uint32_t ntohl __P ((uint32_t __netlong)) __attribute__ ((__const__));
+extern uint16_t ntohs __P ((uint16_t __netshort)) __attribute__ ((__const__));
+extern uint32_t htonl __P ((uint32_t __hostlong)) __attribute__ ((__const__));
+extern uint16_t htons __P ((uint16_t __hostshort)) __attribute__ ((__const__));
 
 #include <endian.h>