diff --git a/bin/tests/rbt_test.c b/bin/tests/rbt_test.c
index fcf8c1e804..bd5286d803 100644
--- a/bin/tests/rbt_test.c
+++ b/bin/tests/rbt_test.c
@@ -19,6 +19,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <unistd.h>
 
 #include <isc/boolean.h>