diff --git a/main.c b/main.c
index 74fb0c2..46ab20d 100644
--- a/main.c
+++ b/main.c
@@ -25,8 +25,6 @@
 #include <sys/capability.h>
 #include <unistd.h>
 
-#include <netid_client.h>  // For MARK_UNSET.
-
 #include "clatd.h"
 #include "common.h"
 #include "config.h"
@@ -34,6 +32,10 @@
 
 #define DEVICEPREFIX "v4-"
 
+// Sync MARK_UNSET from netid_client.h
+// TODO: remove MARK_UNSET definition once argument "-m" is removed.
+#define MARK_UNSET 0u
+
 /* function: stop_loop
  * signal handler: stop the event loop
  */