diff --git a/gnu/packages/commencement.scm b/gnu/packages/commencement.scm
index 73b0ce4364..73b27a290a 100644
--- a/gnu/packages/commencement.scm
+++ b/gnu/packages/commencement.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2014 Andreas Enge <andreas@enge.fr>
 ;;; Copyright © 2012 Nikita Karetnikov <nikita@karetnikov.org>
 ;;; Copyright © 2014, 2015 Mark H Weaver <mhw@netris.org>
@@ -434,7 +434,8 @@ (define static-bash-for-glibc
                                      ("libc" ,glibc-final-with-bootstrap-bash)
                                      ,@(fold alist-delete %boot1-inputs
                                              '("gcc" "libc")))
-                                   (current-source-location)))))
+                                   (current-source-location)
+                                   #:guile %bootstrap-guile))))
 
 (define gettext-boot0
   ;; A minimal gettext used during bootstrap.
diff --git a/guix/build-system/gnu.scm b/guix/build-system/gnu.scm
index c83c50b76e..9c53825c4a 100644
--- a/guix/build-system/gnu.scm
+++ b/guix/build-system/gnu.scm
@@ -96,10 +96,11 @@ (define rewritten-input
     (package (inherit p)
       (location (if (pair? loc) (source-properties->location loc) loc))
       (arguments
-       (let ((args (package-arguments p)))
-         `(#:guile ,guile
-           #:implicit-inputs? #f
-           ,@args)))
+       ;; 'ensure-keyword-arguments' guarantees that this procedure is
+       ;; idempotent.
+       (ensure-keyword-arguments (package-arguments p)
+                                 `(#:guile ,guile
+                                   #:implicit-inputs? #f)))
       (replacement
        (let ((replacement (package-replacement p)))
          (and replacement