diff --git a/gnu/packages/ocaml.scm b/gnu/packages/ocaml.scm
index 8ef6effb1f..7c5a2f939b 100644
--- a/gnu/packages/ocaml.scm
+++ b/gnu/packages/ocaml.scm
@@ -5,7 +5,7 @@
 ;;; Copyright © 2015 David Hashe <david.hashe@dhashe.com>
 ;;; Copyright © 2016 Eric Bavier <bavier@member.fsf.org>
 ;;; Copyright © 2016 Jan Nieuwenhuizen <janneke@gnu.org>
-;;; Copyright © 2016, 2018, 2019 Efraim Flashner <efraim@flashner.co.il>
+;;; Copyright © 2016, 2018, 2019, 2020 Efraim Flashner <efraim@flashner.co.il>
 ;;; Copyright © 2016-2020 Julien Lepiller <julien@lepiller.eu>
 ;;; Copyright © 2017 Ben Woodcroft <donttrustben@gmail.com>
 ;;; Copyright © 2017, 2018, 2019 Tobias Geerinckx-Rice <me@tobias.gr>
@@ -1756,6 +1756,7 @@ through Transport Layer Security (@dfn{TLS}) encrypted connections.")
               (uri (git-reference
                      (url "https://github.com/mirage/mmap")
                      (commit (string-append "v" version))))
+              (file-name (git-file-name name version))
               (sha256
                (base32
                 "1jaismy5d1bhbbanysmr2k79px0yv6ya265dri3949nha1l23i60"))))