diff --git a/lib/prefix.c b/lib/prefix.c
index 29399f6..98b53b1 100644
--- a/lib/prefix.c
+++ b/lib/prefix.c
@@ -917,12 +917,12 @@ prefix_default (const struct prefix *p)
   switch (p->family)
     {
     case AF_INET:
-      return prefix_ipv4_any (p);
+      return prefix_ipv4_any ((const struct prefix_ipv4 *) p);
       break;
 
 #ifdef HAVE_IPV6
     case AF_INET6:
-      return prefix_ipv6_default (p);
+      return prefix_ipv6_default ((const struct prefix_ipv6 *) p);
       break;
 #endif /* HAVE_IPV6 */