diff --git a/src/device.c b/src/device.c
index 9bfaf776d600cc557358748111575f9aa9ec5c1c..4e1abbeb6f25c96ce5a23f4187248239bb0f9b61 100644
--- a/src/device.c
+++ b/src/device.c
@@ -307,7 +307,7 @@ RTM_EXPORT(rt_device_close);
  *
  * @param size is the size of buffer.
  *
- * @return the actually read size on successful, otherwise negative returned.
+ * @return the actually read size on successful, otherwise zero returned.
  *
  * @note since 0.4.0, the unit of size/pos is a block for block device.
  */
@@ -350,7 +350,7 @@ RTM_EXPORT(rt_device_read);
  *
  * @param size is the size of buffer.
  *
- * @return the actually written size on successful, otherwise negative returned.
+ * @return the actually written size on successful, otherwise zero returned.
  *
  * @note since 0.4.0, the unit of size/pos is a block for block device.
  */