2 files changed, 8 insertions, 1 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index e3f34e27dfc..82a9b24876c 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -2,6 +2,8 @@
 
         * nsterm.m (run): Only use non-system event loop if OSX version is
         exactly 10.9 (Bug#18993).
+        (ns_set_vertical_scroll_bar): Don't call bar setPosition: unless
+        needed (Bug#18757).
 
 2014-11-08  Michael Albinus  <michael.albinus@gmx.de>
 
diff --git a/src/nsterm.m b/src/nsterm.m
index 216678357e7..318f14acfc8 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -3759,6 +3759,7 @@ ns_set_vertical_scroll_bar (struct window *window,
   EmacsScroller *bar;
   int window_y, window_height;
   int top, left, height, width;
+  BOOL update_p = YES;
 
   /* optimization; display engine sends WAY too many of these.. */
   if (!NILP (window->vertical_scroll_bar))
@@ -3773,6 +3774,7 @@ ns_set_vertical_scroll_bar (struct window *window,
             }
           else
             view->scrollbarsNeedingUpdate--;
+          update_p = NO;
         }
     }
 
@@ -3814,6 +3816,7 @@ ns_set_vertical_scroll_bar (struct window *window,
 
       bar = [[EmacsScroller alloc] initFrame: r window: win];
       wset_vertical_scroll_bar (window, make_save_ptr (bar));
+      update_p = YES;
     }
   else
     {
@@ -3916,10 +3919,12 @@ ns_set_horizontal_scroll_bar (struct window *window,
           if (oldRect.origin.x != r.origin.x)
               ns_clear_frame_area (f, left, top, width, height);
           [bar setFrame: r];
+          update_p = YES;
         }
     }
 
-  [bar setPosition: position portion: portion whole: whole];
+  if (update_p)
+    [bar setPosition: position portion: portion whole: whole];
   unblock_input ();
 }