diff --git a/src/vnet/l2/l2_fib.h b/src/vnet/l2/l2_fib.h
index 626fbe5..d8b37d2 100644
--- a/src/vnet/l2/l2_fib.h
+++ b/src/vnet/l2/l2_fib.h
@@ -129,6 +129,8 @@
 
 STATIC_ASSERT_SIZEOF (l2fib_entry_result_flags_t, 1);
 
+extern u8 *format_l2fib_entry_result_flags (u8 * s, va_list * args);
+
 /*
  * The l2fib entry results
  */