diff --git a/lisp/calc/calccomp.el b/lisp/calc/calccomp.el
index a59ad82aa57..73a627f178c 100644
--- a/lisp/calc/calccomp.el
+++ b/lisp/calc/calccomp.el
@@ -1656,7 +1656,11 @@ Not all brackets have midpieces.")
 	((memq (car c) '(set break)) t)))
 
 (defun math-comp-width (c)
-  (cond ((not (consp c)) (length c))
+  (cond ((not (consp c))
+         (or (and (stringp c)
+                  (ceiling (string-pixel-width c)
+                           (string-pixel-width "-")))
+             (length c)))
 	((memq (car c) '(horiz subscr supscr))
 	 (let ((accum 0))
 	   (while (setq c (cdr c))