diff --git a/puml-mode.el b/puml-mode.el
index 2d5f31d..06b74d2 100644
--- a/puml-mode.el
+++ b/puml-mode.el
@@ -52,7 +52,7 @@
 
 (defvar puml-mode-hook nil "Standard hook for puml-mode.")
 
-(defvar puml-mode-version "0.6.5" "The puml-mode version string.")
+(defconst puml-mode-version "0.6.5" "The puml-mode version string.")
 
 (defvar puml-mode-debug-enabled nil)