diff --git a/include/freetype/ftincrem.h b/include/freetype/ftincrem.h
index bb636ba49..aaf689ff1 100644
--- a/include/freetype/ftincrem.h
+++ b/include/freetype/ftincrem.h
@@ -117,7 +117,7 @@ FT_BEGIN_HEADER
     FT_Long  bearing_x;
     FT_Long  bearing_y;
     FT_Long  advance;
-    FT_Long  advance_v;
+    FT_Long  advance_v;     /* since 2.3.12 */
 
   } FT_Incremental_MetricsRec;