diff --git a/usr.sbin/rtsold/cap_llflags.c b/usr.sbin/rtsold/cap_llflags.c
index 2b1d31b48444..b2c07df7379d 100644
--- a/usr.sbin/rtsold/cap_llflags.c
+++ b/usr.sbin/rtsold/cap_llflags.c
@@ -44,6 +44,7 @@ __FBSDID("$FreeBSD$");
 #include <errno.h>
 #include <ifaddrs.h>
 #include <string.h>
+#include <unistd.h>
 
 #include <libcasper.h>
 #include <libcasper_service.h>