diff --git a/include/rt_names.h b/include/rt_names.h
index c0ea4f98..921be060 100644
--- a/include/rt_names.h
+++ b/include/rt_names.h
@@ -22,7 +22,7 @@ int inet_proto_a2n(const char *buf);
 
 
 const char * ll_type_n2a(int type, char *buf, int len);
-const char *ll_addr_n2a(unsigned char *addr, int alen,
+const char *ll_addr_n2a(const unsigned char *addr, int alen,
 			int type, char *buf, int blen);
 int ll_addr_a2n(char *lladdr, int len, const char *arg);
 
diff --git a/lib/ll_addr.c b/lib/ll_addr.c
index c12ab075..2ce9abfb 100644
--- a/lib/ll_addr.c
+++ b/lib/ll_addr.c
@@ -29,7 +29,7 @@
 #include "utils.h"
 
 
-const char *ll_addr_n2a(unsigned char *addr, int alen, int type, char *buf, int blen)
+const char *ll_addr_n2a(const unsigned char *addr, int alen, int type, char *buf, int blen)
 {
 	int i;
 	int l;