diff --git a/include/dwarf2.h b/include/dwarf2.h
index 5bc6a92c6c6a..2c1aeb6b912d 100644
--- a/include/dwarf2.h
+++ b/include/dwarf2.h
@@ -333,6 +333,8 @@ enum dwarf_macro_record_type
     DW_MACRO_GNU_define_indirect = 5,
     DW_MACRO_GNU_undef_indirect = 6,
     DW_MACRO_GNU_transparent_include = 7,
+    /* Extensions for DWZ multifile.
+       See http://www.dwarfstd.org/ShowIssue.php?issue=120604.1&type=open .  */
     DW_MACRO_GNU_define_indirect_alt = 8,
     DW_MACRO_GNU_undef_indirect_alt = 9,
     DW_MACRO_GNU_transparent_include_alt = 10,