diff --git a/src/ChangeLog b/src/ChangeLog
index ae99fcc138d..e336e3dfe89 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2012-09-09  Eli Zaretskii  <eliz@gnu.org>
+
+	* dispnew.c (update_window_line): When the left margin area of a
+	screen line is updated, set the redraw_fringe_bitmaps_p flag of
+	that screen line.  (Bug#12277)
+
 2012-09-09  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Assume C89 or later for math functions (Bug#12381).
diff --git a/src/dispnew.c b/src/dispnew.c
index 85b3254aae3..fae415dcaf2 100644
--- a/src/dispnew.c
+++ b/src/dispnew.c
@@ -3951,6 +3951,11 @@ update_window_line (struct window *w, int vpos, bool *mouse_face_overwritten_p)
 	{
 	  changed_p = 1;
 	  update_marginal_area (w, LEFT_MARGIN_AREA, vpos);
+	  /* Setting this flag will ensure the vertical border, if
+	     any, between this window and the one on its left will be
+	     redrawn.  This is necessary because updating the left
+	     margin area can potentially draw over the border.  */
+	  current_row->redraw_fringe_bitmaps_p = 1;
 	}
 
       /* Update the display of the text area.  */