diff --git a/libc/include/net/if.h b/libc/include/net/if.h
index 763ac5b..9044fc5 100644
--- a/libc/include/net/if.h
+++ b/libc/include/net/if.h
@@ -37,5 +37,6 @@
  * Map an interface name into its corresponding index.
  */
 extern unsigned int if_nametoindex(const char *);
+extern char*        if_indextoname(unsigned ifindex, char *ifname);
 
 __END_DECLS