diff --git a/build-aux/build-guile.sh b/build-aux/build-guile.sh
index 73640807..00834fbc 100755
--- a/build-aux/build-guile.sh
+++ b/build-aux/build-guile.sh
@@ -31,6 +31,7 @@ mes/as.scm
 mes/bytevectors.scm
 mes/elf.scm
 mes/guile.scm
+mes/test.scm
 mes/M1.scm"
 
 export srcdir=.
diff --git a/check.sh b/check.sh
index 7c4eb0b3..9c8b2fab 100755
--- a/check.sh
+++ b/check.sh
@@ -41,13 +41,13 @@ tests/cwv.test
 tests/math.test
 tests/vector.test
 tests/srfi-1.test
+tests/srfi-9.test
 tests/srfi-13.test
 tests/srfi-14.test
 tests/srfi-43.test
 tests/optargs.test
 tests/fluids.test
 tests/catch.test
-tests/record.test
 tests/getopt-long.test
 tests/guile.test
 tests/syntax.test
diff --git a/module/mes/test.mes b/module/mes/test.mes
index 97c6e601..eddb5673 100644
--- a/module/mes/test.mes
+++ b/module/mes/test.mes
@@ -25,7 +25,11 @@
 
 ;;; Code:
 
-(mes-use-module (mes base))
+(cond-expand
+ (mes
+  (mes-use-module (mes base)))
+ (else))
+
 (cond-expand
  (mes
   (define mes? #t)
diff --git a/module/mes/test.scm b/module/mes/test.scm
new file mode 100644
index 00000000..2e27db17
--- /dev/null
+++ b/module/mes/test.scm
@@ -0,0 +1,22 @@
+;;; -*-scheme-*-
+
+;;; Mes --- Maxwell Equations of Software
+;;; Copyright © 2018 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+;;;
+;;; This file is part of Mes.
+;;;
+;;; Mes is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; Mes is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Mes.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (mes test))
+(include-from-path "mes/test.mes")
diff --git a/module/srfi/srfi-9.mes b/module/srfi/srfi-9.mes
index b09e2597..47767c9d 100644
--- a/module/srfi/srfi-9.mes
+++ b/module/srfi/srfi-9.mes
@@ -53,9 +53,10 @@
 
 (define (record-getter type field)
   (let ((i (record-field-index type field)))
-    (lambda (o)
+    (lambda (o . field?)
       (if (not (eq? (record-type o) type)) (error "record getter: record expected" type o)
-          (vector-ref o i)))))
+          (if (pair? field?) field
+              (vector-ref o i))))))
 
 (define (record-setter type field)
   (let ((i (record-field-index type field)))
diff --git a/module/srfi/srfi-9/gnu.mes b/module/srfi/srfi-9/gnu.mes
new file mode 100644
index 00000000..8bdad798
--- /dev/null
+++ b/module/srfi/srfi-9/gnu.mes
@@ -0,0 +1,37 @@
+;;; -*-scheme-*-
+
+;;; Mes --- Maxwell Equations of Software
+;;; Copyright © 2017,2018 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+;;;
+;;; This file is part of Mes.
+;;;
+;;; Mes is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; Mes is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Mes.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;; srfi-9.mes - GNU immutable records.
+
+(define-macro (define-immutable-record-type type constructor+params predicate . fields)
+  `(define-record-type ,type ,constructor+params ,predicate ,@(map (lambda (f) (list-head f 2)) fields)))
+
+(define-macro (set-field o getters value)
+  `(let ((getter ,(car getters)))
+     (let ((type (record-type ,o))
+           (set (getter ,o #t)))
+       (define (field->value field)
+         (if (eq? set field) ,value
+             ((record-getter type field) ,o)))
+       (let* ((fields (record-fields type))
+              (values (map field->value fields)))
+         (apply (record-constructor type fields) values)))))
diff --git a/tests/record.test b/tests/srfi-9.test
similarity index 76%
rename from tests/record.test
rename to tests/srfi-9.test
index 97e9471b..799c671a 100755
--- a/tests/record.test
+++ b/tests/srfi-9.test
@@ -25,14 +25,16 @@ exit $?
 ;;; You should have received a copy of the GNU General Public License
 ;;; along with Mes.  If not, see <http://www.gnu.org/licenses/>.
 
-(mes-use-module (srfi srfi-0))
-(mes-use-module (srfi srfi-9))
-(mes-use-module (mes test))
 
 (cond-expand
+ (mes
+  (mes-use-module (srfi srfi-9))
+  (mes-use-module (srfi srfi-9 gnu))
+  (mes-use-module (mes test)))
  (guile
-  (use-modules (srfi srfi-9)))
- (mes))
+  (use-modules (srfi srfi-9))
+  (use-modules (srfi srfi-9 gnu))
+  (use-modules (mes test))))
 
 (pass-if "first dummy" #t)
 (pass-if-not "second dummy" #f)
@@ -47,4 +49,8 @@ exit $?
 (pass-if "record"
   (lexical-token? (make-lexical-token 'x 'y 'z)))
 
+(pass-if-equal "set-field" "baar"
+         (let ((token (make-lexical-token 'foo "bar" 'baz)))
+           (lexical-token-category (set-field token (lexical-token-category) "baar"))))
+
 (result 'report)
diff --git a/tests/record.test-guile b/tests/srfi-9.test-guile
similarity index 100%
rename from tests/record.test-guile
rename to tests/srfi-9.test-guile