diff --git a/sys/netinet/in.c b/sys/netinet/in.c
index 6f408eb92860..a656102da0e7 100644
--- a/sys/netinet/in.c
+++ b/sys/netinet/in.c
@@ -34,6 +34,7 @@
 __FBSDID("$FreeBSD$");
 
 #include "opt_carp.h"
+#include "opt_route.h"
 
 #include <sys/param.h>
 #include <sys/systm.h>