diff --git a/tests/Makefile.am b/tests/Makefile.am
index be04df3..a8327d6 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -1,44 +1,49 @@
 # Makefile.am for libgpg-error/tests.
 # Copyright (C) 2003 g10 Code GmbH
 #
 # This file is part of libgpg-error.
 #
 # libgpg-error is free software; you can redistribute it and/or modify
 # it under the terms of the GNU Lesser General Public License as
 # published by the Free Software Foundation; either version 2.1 of the
 # License, or (at your option) any later version.
 #
 # libgpg-error 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 Lesser General Public License for more details.
 #
 # You should have received a copy of the GNU Lesser General Public
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 
 ## Process this file with automake to produce Makefile.in
 
 if HAVE_W32CE_SYSTEM
 extra_includes = -idirafter $(top_builddir)/src/gpg-extra
 else
 extra_includes =
 endif
 
 EXTRA_DIST = t-argparse.conf etc/t-argparse.conf
 
 gpg_error_lib = ../src/libgpg-error.la
 
 TESTS = t-version t-strerror t-syserror t-lock t-printf t-poll t-b64 \
 	t-argparse t-logging t-stringutils t-malloc
 
+if HAVE_W32_SYSTEM
+else
+TESTS += t-lock-single-posix
+endif
+
 AM_CPPFLAGS = -I$(top_builddir)/src $(extra_includes)
 
 AM_LDFLAGS = -no-install
 LDADD = $(gpg_error_lib) @LDADD_FOR_TESTS_KLUDGE@
 
 noinst_PROGRAMS = $(TESTS)
 noinst_HEADERS = t-common.h
 
 t_lock_LDADD = $(LDADD) $(LIBMULTITHREAD)
 t_poll_LDADD = $(LDADD) $(LIBMULTITHREAD)
diff --git a/tests/t-lock-single-posix.c b/tests/t-lock-single-posix.c
new file mode 100644
index 0000000..e3432b1
--- /dev/null
+++ b/tests/t-lock-single-posix.c
@@ -0,0 +1,165 @@
+/* t-lock-single-posix.c - Check the lock functions with single thread
+ * Copyright (C) 2021 g10 Code GmbH
+ *
+ * This file is part of libgpg-error.
+ *
+ * libgpg-error is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * as published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * libgpg-error 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this program; if not, see <https://www.gnu.org/licenses/>.
+ */
+
+#if HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#define PGM "t-lock-single"
+
+#include "t-common.h"
+
+GPGRT_LOCK_DEFINE (the_lock);
+
+static int locking_used;
+
+#ifdef USE_POSIX_THREADS_FROM_LIBC
+#include <pthread.h>
+
+static void *
+thread_func (void *arg)
+{
+  (void)arg;
+  return NULL;
+}
+#endif
+
+static void
+run_test (void)
+{
+  gpg_err_code_t rc;
+
+  rc = gpgrt_lock_lock (&the_lock);
+  if (rc)
+    fail ("gpgrt_lock_lock failed at %d: %s", __LINE__, gpg_strerror (rc));
+
+  rc = gpgrt_lock_unlock (&the_lock);
+  if (rc)
+    fail ("gpgrt_lock_unlock failed at %d: %s", __LINE__,gpg_strerror (rc));
+
+  if (locking_used)
+    /*It was incremented, even with single thread.  */
+    fail ("Single thread situation is not correctly handled\n");
+
+#ifdef USE_POSIX_THREADS_FROM_LIBC
+  /*
+   * With !USE_POSIX_THREADS_FROM_LIBC, it is determined at link time.
+   *
+   * With USE_POSIX_THREADS_FROM_LIBC, it is determined at runtime,
+   * and the condition is changed when an application actually uses
+   * thread.
+   */
+  {
+    pthread_t rthread;
+    pthread_create (&rthread, NULL, thread_func, NULL);
+
+    rc = gpgrt_lock_lock (&the_lock);
+    if (rc)
+      fail ("gpgrt_lock_lock failed at %d: %s", __LINE__, gpg_strerror (rc));
+
+    rc = gpgrt_lock_unlock (&the_lock);
+    if (rc)
+      fail ("gpgrt_lock_unlock failed at %d: %s", __LINE__,gpg_strerror (rc));
+
+    pthread_join (rthread, NULL);
+
+    if (!locking_used)
+      /*It was *NOT* incremented, even with multiple threads.  */
+      fail ("Multiple threads situation is not correctly handled\n");
+  }
+#endif
+}
+
+
+static void
+syscall_clam_pre (void)
+{
+  if (debug)
+    show ("syscall pre called\n");
+  locking_used++;
+}
+
+static void
+syscall_clam_post (void)
+{
+  if (debug)
+    show ("syscall post called\n");
+}
+
+int
+main (int argc, char **argv)
+{
+  int last_argc = -1;
+  int rc;
+
+  if (argc)
+    {
+      argc--; argv++;
+    }
+  while (argc && last_argc != argc )
+    {
+      last_argc = argc;
+      if (!strcmp (*argv, "--help"))
+        {
+          puts (
+"usage: ./t-lock-single [options]\n"
+"\n"
+"Options:\n"
+"  --verbose      Show what is going on\n"
+"  --debug        Flyswatter\n"
+);
+          exit (0);
+        }
+      if (!strcmp (*argv, "--verbose"))
+        {
+          verbose = 1;
+          argc--; argv++;
+        }
+      else if (!strcmp (*argv, "--debug"))
+        {
+          verbose = debug = 1;
+          argc--; argv++;
+        }
+    }
+
+  if (!gpg_error_check_version (GPG_ERROR_VERSION))
+    {
+      die ("gpg_error_check_version returned an error");
+      errorcount++;
+    }
+
+  gpgrt_set_syscall_clamp (syscall_clam_pre, syscall_clam_post);
+
+  rc = gpgrt_lock_init (&the_lock);
+  if (rc)
+    fail ("gpgrt_lock_init failed at %d: %s", __LINE__, gpg_strerror (rc));
+
+  run_test ();
+
+  gpgrt_lock_destroy (&the_lock);
+
+  return errorcount ? 1 : 0;
+}