diff --git a/asdf.lisp b/asdf.lisp
index 100b8c9..ea1cd1e 100644
--- a/asdf.lisp
+++ b/asdf.lisp
@@ -161,7 +161,7 @@
 ;;;; -------------------------------------------------------------------------
 ;;;; User-visible parameters
 ;;;;
-(defvar *asdf-revision*
+(defparameter *asdf-revision*
   ;; the 1+ hair is to ensure that we don't do an inadvertent find and replace
   (subseq "REVISION:1.372" (1+ (length "REVISION"))))