diff --git a/graphics/mapper/4.0/IMapper.hal b/graphics/mapper/4.0/IMapper.hal
index 85c7c81..46506f5 100644
--- a/graphics/mapper/4.0/IMapper.hal
+++ b/graphics/mapper/4.0/IMapper.hal
@@ -219,7 +219,8 @@
      *     - `BAD_BUFFER` if the buffer is invalid or is incompatible with this
      *       function.
      *     - `BAD_VALUE` if @p cpuUsage is 0, contains non-CPU usage flags, or
-     *       is incompatible with the buffer.
+     *       is incompatible with the buffer. Also if the @p accessRegion is
+     *       outside the bounds of the buffer or the accessRegion is invalid.
      *     - `NO_RESOURCES` if the buffer cannot be locked at this time. Note
      *       that locking may succeed at a later time.
      * @return data CPU-accessible pointer to the buffer data.