diff --git a/include/ucore/utils.h b/include/ucore/utils.h
index cc23bef..e70327c 100644
--- a/include/ucore/utils.h
+++ b/include/ucore/utils.h
@@ -109,8 +109,10 @@ do {\
 while (0)
 
 /**
- * Round up X / y
- * 
+ * Round up x / y
+ * (e.g 100/9 == 12, 3/2 == 2)
+ * x + y must not overflow.
+ *
  * @param x numerator, must be positive
  * @param y denominator
  * @return x/y rounded up