Stop using TRUE and FALSE for exit status.
diff --git a/tty.c b/tty.c
index 6eebed9..46201d3 100644
--- a/tty.c
+++ b/tty.c
@@ -38,5 +38,5 @@
 		else
 			puts("not a tty");
 	}
-	return(isatty(0) ? TRUE : FALSE);
+	return(isatty(0) ? EXIT_SUCCESS : EXIT_FAILURE);
 }