(try_window_id): Don't use XFASTINT as an lvalue.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index 28a3b868da0..7f3d05deec4 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -1590,7 +1590,8 @@ try_window_id (window)
       if (i == xp.bufpos)
         return -2;
 
-      XFASTINT (w->window_end_vpos) += scroll_amount;
+      XSETFASTINT (w->window_end_vpos,
+                   XFASTINT (w->window_end_vpos) + scroll_amount);
 
       /* Before doing any scrolling, verify that point will be on frame. */
       if (PT > ep.bufpos && !(PT <= xp.bufpos && xp.bufpos < height))
@@ -1796,7 +1797,8 @@ try_window_id (window)
           val = *vmotion (Z - XFASTINT (w->window_end_pos),
                           delta, width, hscroll, window);
           XSETFASTINT (w->window_end_pos, Z - val.bufpos);
-          XFASTINT (w->window_end_vpos) += val.vpos;
+          XSETFASTINT (w->window_end_vpos,
+                       XFASTINT (w->window_end_vpos) + val.vpos);
         }
     }