diff --git a/sw/device/lib/flash_ctrl.h b/sw/device/lib/flash_ctrl.h
index 00b6640..381d061 100644
--- a/sw/device/lib/flash_ctrl.h
+++ b/sw/device/lib/flash_ctrl.h
@@ -86,7 +86,7 @@
  * @param addr Read start address.
  * @param part Flash parittion to access.
  * @param size Number of 4B words to read.
- * @param data Output buffer.
+ * @param[out] data Output buffer.
  * @return Non zero on failure.
  */
 int flash_read(uint32_t addr, part_type_t part, uint32_t size, uint32_t *data);