diff --git a/src/conf/nwfilter_conf.c b/src/conf/nwfilter_conf.c
index f4af1267ec..336ea3b890 100644
--- a/src/conf/nwfilter_conf.c
+++ b/src/conf/nwfilter_conf.c
@@ -33,6 +33,7 @@
 #if HAVE_NET_ETHERNET_H
 # include <net/ethernet.h>
 #endif
+#include <unistd.h>
 
 #include "internal.h"