diff --git a/test/t_arith.h b/test/t_arith.h
index 99b24f4..2f88c7c 100644
--- a/test/t_arith.h
+++ b/test/t_arith.h
@@ -2,6 +2,7 @@
 
 #include "test.h"
 
+/* tests arithmetic shift for signed integers (rather than logical shift) */
 int test_sar(void *dat) {
 	(void)dat;
 	return assert_true(-3 >> 5 == -1);