diff --git a/gnu/packages/admin.scm b/gnu/packages/admin.scm
index 5c7e41f51b..f499a1252b 100644
--- a/gnu/packages/admin.scm
+++ b/gnu/packages/admin.scm
@@ -941,10 +941,10 @@ to allow automatic login and starting any app.")
                       (use-modules (guix build utils)
                                    (srfi srfi-26))
 
-                      (let* ((source (assoc-ref %build-inputs "source"))
-                             (tar    (assoc-ref %build-inputs "tar"))
-                             (xz     (assoc-ref %build-inputs "xz"))
-                             (output (assoc-ref %outputs "out"))
+                      (let* ((source #+(package-source this-package))
+                             (tar    #+(this-package-native-input "tar"))
+                             (xz     #+(this-package-native-input "xz"))
+                             (output #$output)
                              (etc    (string-append output "/etc")))
                         (setenv "PATH" (string-append xz "/bin"))
                         (invoke (string-append tar "/bin/tar") "xvf"