diff --git a/gnu/packages/certs.scm b/gnu/packages/certs.scm
index 30e53e3458..2b5ea3850a 100644
--- a/gnu/packages/certs.scm
+++ b/gnu/packages/certs.scm
@@ -3,7 +3,7 @@
 ;;; Copyright © 2015 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2016, 2017 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2017 Leo Famulari <leo@famulari.name>
-;;; Copyright © 2017 Tobias Geerinckx-Rice <me@tobias.gr>
+;;; Copyright © 2017, 2018 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -102,8 +102,10 @@
                   (srfi srfi-26)
                   (ice-9 regex))
        #:phases
-         (alist-cons-after
-           'unpack 'install
+       (modify-phases
+           (map (cut assq <> %standard-phases)
+                '(set-paths install-locale unpack))
+         (add-after 'unpack 'install
            (lambda _
              (let ((certsdir (string-append %output "/etc/ssl/certs/"))
                    (trusted-rx (make-regexp "^# openssl-trust=[a-zA-Z]"
@@ -131,10 +133,9 @@
                  ;; "Usage error; try -help."
                  ;; This looks like a bug in openssl-1.0.2, but we can also
                  ;; switch into the target directory.
-                 (system* "c_rehash" "."))))
+                 (invoke "c_rehash" "."))
+               #t))))))
 
-           (map (cut assq <> %standard-phases)
-                '(set-paths install-locale unpack)))))
     (synopsis "CA certificates from Mozilla")
     (description
      "This package provides certificates for Certification Authorities (CA)