diff --git a/src/mesa/pipe/draw/draw_private.h b/src/mesa/pipe/draw/draw_private.h
index 7e5d5db5ab9..b7811e891e7 100644
--- a/src/mesa/pipe/draw/draw_private.h
+++ b/src/mesa/pipe/draw/draw_private.h
@@ -192,7 +192,7 @@ struct draw_context
    /* Post-tnl vertex cache:
     */
    struct {
-      unsigned referenced;
+      unsigned referenced;  /**< bitfield */
       unsigned idx[VCACHE_SIZE + VCACHE_OVERFLOW];
       struct vertex_header *vertex[VCACHE_SIZE + VCACHE_OVERFLOW];
       unsigned overflow;