1 files changed, 10 insertions, 9 deletions

diff --git a/lisp/mouse.el b/lisp/mouse.el
index 3a22fb49b04..c399515a3d2 100644
--- a/lisp/mouse.el
+++ b/lisp/mouse.el
@@ -538,19 +538,20 @@ resized by dragging their header-line."
          (echo-keystrokes 0)
          (start-event-frame (window-frame (car (car (cdr start-event)))))
          (start-event-window (car (car (cdr start-event))))
-         (start-nwindows (count-windows t))
          event mouse x left right edges wconfig growth
          (which-side
           (or (cdr (assq 'vertical-scroll-bars (frame-parameters start-event-frame)))
               'right)))
-    (if (one-window-p t)
-        (error "Attempt to resize sole ordinary window"))
-    (if (eq which-side 'right)
-        (if (= (nth 2 (window-edges start-event-window))
-               (frame-width start-event-frame))
-            (error "Attempt to drag rightmost scrollbar"))
-      (if (= (nth 0 (window-edges start-event-window)) 0)
-          (error "Attempt to drag leftmost scrollbar")))
+    (cond
+     ((one-window-p t)
+      (error "Attempt to resize sole ordinary window"))
+     ((and (eq which-side 'right)
+           (>= (nth 2 (window-inside-edges start-event-window))
+               (frame-width start-event-frame)))
+      (error "Attempt to drag rightmost scrollbar"))
+     ((and (eq which-side 'left)
+           (= (nth 0 (window-inside-edges start-event-window)) 0))
+      (error "Attempt to drag leftmost scrollbar")))
     (track-mouse
       (progn
         ;; enlarge-window only works on the selected window, so