1 files changed, 6 insertions, 3 deletions

diff --git a/src/window.c b/src/window.c
index afb8f75537b..c8fcb3a607f 100644
--- a/src/window.c
+++ b/src/window.c
@@ -6575,9 +6575,12 @@ and redisplay normally--don't erase and redraw the frame.  */)
      in case scroll_margin is buffer-local.  */
   this_scroll_margin = window_scroll_margin (w, MARGIN_IN_LINES);
 
-  /* Don't use redisplay code for initial frames, as the necessary
-     data structures might not be set up yet then.  */
-  if (!FRAME_INITIAL_P (XFRAME (w->frame)))
+  /* Don't use the display code for initial frames, as the necessary
+     data structures might not be set up yet then.  Also don't use it
+     for buffers with very long lines, as it tremdously slows down
+     redisplay, especially when lines are truncated.  */
+  if (!FRAME_INITIAL_P (XFRAME (w->frame))
+      && !current_buffer->long_line_optimizations_p)
     {
       specpdl_ref count = SPECPDL_INDEX ();