diff --git a/guix/packages.scm b/guix/packages.scm
index c955b35..7c2788c 100644
--- a/guix/packages.scm
+++ b/guix/packages.scm
@@ -445,7 +445,7 @@ IMPORTED-MODULES specify modules to use/import for use by SNIPPET."
 
           ;; SOURCE may be either a directory or a tarball.
           (and (if (file-is-directory? #+source)
-                   (let* ((store     (or (getenv "NIX_STORE") "/gnu/store"))
+                   (let* ((store     (%store-directory))
                           (len       (+ 1 (string-length store)))
                           (base      (string-drop #+source len))
                           (dash      (string-index base #\-))