diff --git a/lisp/image-mode.el b/lisp/image-mode.el
index 1820defa195..336d89dd52d 100644
--- a/lisp/image-mode.el
+++ b/lisp/image-mode.el
@@ -248,8 +248,9 @@ Stop if the right edge of the image is reached."
 	 (image-set-window-hscroll (max 0 (+ (window-hscroll) n))))
 	(t
 	 (let* ((image (image-get-display-property))
-		(edges (window-inside-edges))
-		(win-width (- (nth 2 edges) (nth 0 edges)))
+		(edges (window-edges nil t nil t))
+		(win-width (- (/ (nth 2 edges) (frame-char-width))
+                              (/ (nth 0 edges) (frame-char-width))))
 		(img-width (ceiling (car (image-display-size image)))))
 	   (image-set-window-hscroll (min (max 0 (- img-width win-width))
 					  (+ n (window-hscroll))))))))