diff --git a/sys/net/if_dl.h b/sys/net/if_dl.h
--- a/sys/net/if_dl.h
+++ b/sys/net/if_dl.h
@@ -32,6 +32,8 @@
 #ifndef _NET_IF_DL_H_
 #define _NET_IF_DL_H_
 
+#include <sys/types.h>
+
 /*
  * A Link-Level Sockaddr may specify the interface in one of two
  * ways: either by means of a system-provided index number (computed