diff --git a/clutter/glx/clutter-stage-glx.c b/clutter/glx/clutter-stage-glx.c
index 8ca0b9d..60b7ebb 100644
--- a/clutter/glx/clutter-stage-glx.c
+++ b/clutter/glx/clutter-stage-glx.c
@@ -642,6 +642,12 @@ clutter_stage_glx_redraw (ClutterStageGLX *stage_glx,
        * we have to manually wait for the vblank period...
        */

+      /* Here 'is_synchronized' only means that the blit won't cause a
+       * tear, ie it won't prevent multiple blits per retrace if they
+       * can all be performed in the blanking period. If that's the
+       * case then we still want to use the vblank sync menchanism but
+       * we only need it to throttle redraws.
+       */
       if (!backend_glx->blit_sub_buffer_is_synchronized)
         {
           /* XXX: note that glXCopySubBuffer, at least for Intel, is