diff --git a/plantuml-mode.el b/plantuml-mode.el
index 7e512a8..687ed3a 100644
--- a/plantuml-mode.el
+++ b/plantuml-mode.el
@@ -266,7 +266,7 @@ Uses prefix (as PREFIX) to choose where to display it:
 - 16 (when prefixing the command with C-u C-u) -> new frame.
 - else -> new buffer"
   (interactive "p")
-  (if (mark)
+  (if mark-active
       (plantuml-preview-region prefix)
       (plantuml-preview-buffer prefix)))