diff --git a/t-child.scm b/t-child.scm
index 93208f4..fd1dcc3 100644
--- a/t-child.scm
+++ b/t-child.scm
@@ -1,118 +1,118 @@
 ;; Tests for the low-level process and IPC primitives.
 ;;
 ;; Copyright (C) 2016 g10 Code GmbH
 ;;
 ;; This file is part of GnuPG.
 ;;
 ;; GnuPG 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.
 ;;
 ;; GnuPG 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 this program; if not, see <http://www.gnu.org/licenses/>.
 
 (echo "Testing process and IPC primitives...")
 
 (define (qualify executable)
   (string-append executable (getenv "EXEEXT")))
 
 (define child (qualify "t-child"))
 
 (assert (= 0 (call `(,(qualify "t-child") "return0"))))
 (assert (= 1 (call `(,(qualify "t-child") "return1"))))
 (assert (= 77 (call `(,(qualify "t-child") "return77"))))
 
 (let ((r (call-with-io `(,(qualify "t-child") "return0") "")))
   (assert (= 0 (:retcode r)))
   (assert (string=? "" (:stdout r)))
   (assert (string=? "" (:stderr r))))
 
 (let ((r (call-with-io `(,(qualify "t-child") "return1") "")))
   (assert (= 1 (:retcode r)))
   (assert (string=? "" (:stdout r)))
   (assert (string=? "" (:stderr r))))
 
 (let ((r (call-with-io `(,(qualify "t-child") "return77") "")))
   (assert (= 77 (:retcode r)))
   (assert (string=? "" (:stdout r)))
   (assert (string=? "" (:stderr r))))
 
 (let ((r (call-with-io `(,(qualify "t-child") "hello_stdout") "")))
   (assert (= 0 (:retcode r)))
   (assert (string=? "hello" (:stdout r)))
   (assert (string=? "" (:stderr r))))
 
 (let ((r (call-with-io `(,(qualify "t-child") "hello_stderr") "")))
   (assert (= 0 (:retcode r)))
   (assert (string=? "" (:stdout r)))
   (assert (string=? "hello" (:stderr r))))
 
 (let ((r (call-with-io `(,(qualify "t-child") "stdout4096") "")))
   (assert (= 0 (:retcode r)))
   (assert (= 4096 (string-length (:stdout r))))
   (assert (string=? "" (:stderr r))))
 
 (let ((r (call-with-io `(,(qualify "t-child") "stdout8192") "")))
   (assert (= 0 (:retcode r)))
   (assert (= 8192 (string-length (:stdout r))))
   (assert (string=? "" (:stderr r))))
 
 (let ((r (call-with-io `(,(qualify "t-child") "cat") "hellohello")))
   (assert (= 0 (:retcode r)))
   (assert (string=? "hellohello" (:stdout r)))
   (assert (string=? "" (:stderr r))))
 
 (define (spawn what)
   (spawn-process-fd what CLOSED_FD STDOUT_FILENO STDERR_FILENO))
 
 (let ((pid0 (spawn `(,(qualify "t-child") "return0")))
       (pid1 (spawn `(,(qualify "t-child") "return0"))))
   (assert (equal? '(0 0)
 		  (wait-processes '("child0" "child1") (list pid0 pid1) #t))))
 
 (let ((pid0 (spawn `(,(qualify "t-child") "return1")))
       (pid1 (spawn `(,(qualify "t-child") "return0"))))
   (assert (equal? '(1 0)
 		  (wait-processes '("child0" "child1") (list pid0 pid1) #t))))
 
 (let ((pid0 (spawn `(,(qualify "t-child") "return0")))
       (pid1 (spawn `(,(qualify "t-child") "return77")))
       (pid2 (spawn `(,(qualify "t-child") "return1"))))
   (assert (equal? '(0 77 1)
 		  (wait-processes '("child0" "child1" "child2")
 				  (list pid0 pid1 pid2) #t))))
 
 (let* ((p (pipe))
        (pid0 (spawn-process-fd
 	       `(,(qualify "t-child") "hello_stdout")
 	       CLOSED_FD (:write-end p) STDERR_FILENO))
        (_ (close (:write-end p)))
        (pid1 (spawn-process-fd
 	       `(,(qualify "t-child") "cat")
 	       (:read-end p) STDOUT_FILENO STDERR_FILENO)))
   (close (:read-end p))
   (assert
    (equal? '(0 0)
 	   (wait-processes '("child0" "child1") (list pid0 pid1) #t))))
 (echo " world.")
 
 (tr:do
  (tr:pipe-do
   (pipe:spawn `(,child stdout4096))
   (pipe:spawn `(,child cat)))
  (tr:call-with-content (lambda (c)
-			 (assert (= 4096 (length c))))))
+			 (assert (= 4096 (string-length c))))))
 (tr:do
  (tr:pipe-do
   (pipe:spawn `(,child stdout8192))
   (pipe:spawn `(,child cat)))
  (tr:call-with-content (lambda (c)
-			 (assert (= 8192 (length c))))))
+			 (assert (= 8192 (string-length c))))))
 
 (echo "All good.")