diff --git a/src/vnet/fib/fib_api.h b/src/vnet/fib/fib_api.h
index 0c59531..9eac62f 100644
--- a/src/vnet/fib/fib_api.h
+++ b/src/vnet/fib/fib_api.h
@@ -51,6 +51,7 @@
                                   fib_entry_flag_t entry_flags,
                                   fib_route_path_t *rpaths);
 
+extern u8 *format_vl_api_address_union (u8 * s, va_list * args);
 extern u8* format_vl_api_fib_path(u8 * s, va_list * args);