diff --git a/lisp/emacs-lisp/re-builder.el b/lisp/emacs-lisp/re-builder.el
index 46b429ce6f..84018f06ac 100644
--- a/lisp/emacs-lisp/re-builder.el
+++ b/lisp/emacs-lisp/re-builder.el
@@ -369,7 +369,8 @@ re-builder
             (get-buffer-create reb-buffer)
             `((display-buffer-in-direction)
               (direction . ,dir)
-              (dedicated . t))))))
+              (dedicated . t)
+              (window-height . fit-window-to-buffer))))))
     (font-lock-mode 1)
     (reb-initialize-buffer)))