diff --git a/lisp/calc/calccomp.el b/lisp/calc/calccomp.el
index 73a627f178c..86a2c405272 100644
--- a/lisp/calc/calccomp.el
+++ b/lisp/calc/calccomp.el
@@ -1558,8 +1558,12 @@ Not all brackets have midpieces.")
 	   (setq c (cdr c))
 	   (while (setq c (cdr c))
 	     (if (eq (car-safe (car c)) 'rule)
-		 (math-comp-add-string (make-string maxwid (nth 1 (car c)))
-				       math-comp-hpos math-comp-vpos)
+                 (let* ((sep (nth 1 (car c)))
+                        (rule-width (ceiling
+                                     (* maxwid (string-pixel-width "-"))
+                                     (string-pixel-width (char-to-string sep)))))
+                   (math-comp-add-string (make-string rule-width sep)
+                                         math-comp-hpos math-comp-vpos))
 	       (let ((math-comp-hpos (+ math-comp-hpos (/ (* bias (- maxwid
 							   (car widths)))
 						2))))