--- a/lisp/window.el
+++ b/lisp/window.el
@@ -2730,13 +2730,14 @@ window--resize-mini-window
     (let* ((frame (window-frame window))
 	   (root (frame-root-window frame))
 	   (height (window-pixel-height window))
-	   (min-delta
+           (char-height (frame-char-height frame))
+           (min-delta
 	    (- (window-pixel-height root)
 	       (window-min-size root nil nil t))))
       ;; Sanitize DELTA.
       (cond
-       ((<= (+ height delta) 0)
-	(setq delta (- (frame-char-height (window-frame window)) height)))
+       ((<= (+ height delta) char-height)
+	(setq delta (- char-height height)))
        ((> delta min-delta)
 	(setq delta min-delta)))