diff --git a/lib/if.h b/lib/if.h
index 47e992c..0f088a9 100644
--- a/lib/if.h
+++ b/lib/if.h
@@ -183,12 +183,12 @@
 /* Prototypes. */
 int if_cmp_func (struct interface *, struct interface *);
 struct interface *if_new (void);
-struct interface *if_create (char *name, int namelen);
+struct interface *if_create (const char *name, int namelen);
 struct interface *if_lookup_by_index (unsigned int);
-struct interface *if_lookup_by_name (char *);
+struct interface *if_lookup_by_name (const char *);
 struct interface *if_lookup_exact_address (struct in_addr);
 struct interface *if_lookup_address (struct in_addr);
-struct interface *if_get_by_name (char *);
+struct interface *if_get_by_name (const char *);
 void if_delete (struct interface *);
 int if_is_up (struct interface *);
 int if_is_running (struct interface *);