diff --git a/qemu/include/qapi/error.h b/qemu/include/qapi/error.h
index b3061ebd..3a328cb3 100644
--- a/qemu/include/qapi/error.h
+++ b/qemu/include/qapi/error.h
@@ -172,6 +172,9 @@ void error_setg_internal(Error **errp,
  * Just like error_setg(), with @os_error info added to the message.
  * If @os_error is non-zero, ": " + strerror(os_error) is appended to
  * the human-readable error message.
+ *
+ * The value of errno (which usually can get clobbered by almost any
+ * function call) will be preserved.
  */
 #define error_setg_errno(errp, os_error, fmt, ...)                      \
     error_setg_errno_internal((errp), __FILE__, __LINE__, __func__,     \