diff --git a/src/vnet/adj/rewrite.h b/src/vnet/adj/rewrite.h
index 496bb14..4234986 100644
--- a/src/vnet/adj/rewrite.h
+++ b/src/vnet/adj/rewrite.h
@@ -67,6 +67,8 @@
   VNET_REWRITE_FIXUP_FLOW_HASH = (1 << 2),
 } __attribute__ ((packed)) vnet_rewrite_flags_t;
 
+extern u8 *format_vnet_rewrite_flags (u8 *s, va_list *ap);
+
 typedef struct vnet_rewrite_header_t_
 {
   /* Interface to mark re-written packets with. */