diff --git a/asdf.lisp b/asdf.lisp
index 02fb738e1fbce923215d0fa0c273fe2dae591b07..4e935e562812bf9356f5844e2722d41c30900839 100644
--- a/asdf.lisp
+++ b/asdf.lisp
@@ -262,7 +262,7 @@
            #:clear-source-registry
            #:ensure-source-registry
            #:process-source-registry))
-        (eval `(defvar ,(intern (string versym) (find-package :asdf)) ,asdf-version))))))
+        (eval `(defparameter ,(intern (string versym) (find-package :asdf)) ,asdf-version))))))
 
 (in-package #:asdf)