diff --git a/src/unistd/isatty.c b/src/unistd/isatty.c
index 75a9c186..21222eda 100644
--- a/src/unistd/isatty.c
+++ b/src/unistd/isatty.c
@@ -6,8 +6,6 @@
 int isatty(int fd)
 {
 	struct winsize wsz;
-	unsigned long r = syscall(SYS_ioctl, fd, TIOCGWINSZ, &wsz);
-	if (r == 0) return 1;
-	if (errno != EBADF) errno = ENOTTY;
-	return 0;
+	/* +1 converts from error status (0/-1) to boolean (1/0) */
+	return syscall(SYS_ioctl, fd, TIOCGWINSZ, &wsz) + 1;
 }