diff --git a/lib/isc/include/isc/ipv6.h b/lib/isc/include/isc/ipv6.h
index 7bb5d7b987..36606442af 100644
--- a/lib/isc/include/isc/ipv6.h
+++ b/lib/isc/include/isc/ipv6.h
@@ -66,8 +66,8 @@ struct in6_addr {
 #define IN6ADDR_ANY_INIT 	{{{ 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 }}}
 #define IN6ADDR_LOOPBACK_INIT 	{{{ 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1 }}}
 
-extern struct in6_addr in6addr_any;
-extern struct in6_addr in6addr_loopback;
+extern const struct in6_addr in6addr_any;
+extern const struct in6_addr in6addr_loopback;
 
 struct sockaddr_in6 {
 #ifdef ISC_PLATFORM_HAVESALEN
diff --git a/lib/isc/unix/ipv6.c b/lib/isc/unix/ipv6.c
index 54f2b5de4e..e3342f6e5e 100644
--- a/lib/isc/unix/ipv6.c
+++ b/lib/isc/unix/ipv6.c
@@ -17,5 +17,5 @@
 
 #include <isc/ipv6.h>
 
-struct in6_addr in6addr_any = IN6ADDR_ANY_INIT;
-struct in6_addr in6addr_loopback = IN6ADDR_LOOPBACK_INIT;
+const struct in6_addr in6addr_any = IN6ADDR_ANY_INIT;
+const struct in6_addr in6addr_loopback = IN6ADDR_LOOPBACK_INIT;