diff --git a/tools/regression/lib/libc/stdio/test-perror.c b/tools/regression/lib/libc/stdio/test-perror.c
index 992b734dfa3..24aca895e18 100644
--- a/tools/regression/lib/libc/stdio/test-perror.c
+++ b/tools/regression/lib/libc/stdio/test-perror.c
@@ -40,6 +40,7 @@ __FBSDID("$FreeBSD$");
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 static void cleanup(void);
 static char tmpfil[PATH_MAX];