diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
index 1ad41c5..5b8d931 100644
--- a/nptl/nptl-init.c
+++ b/nptl/nptl-init.c
@@ -36,6 +36,7 @@
 #include <lowlevellock.h>
 #include <kernel-features.h>
 #include <libc-internal.h>
+#include <pthread-pids.h>
 
 #ifndef TLS_MULTIPLE_THREADS_IN_TCB
 /* Pointer to the corresponding variable in libc.  */
@@ -311,10 +312,7 @@ __pthread_initialize_minimal_internal (void)
 
   /* Minimal initialization of the thread descriptor.  */
   struct pthread *pd = THREAD_SELF;
-#ifdef __NR_set_tid_address
-  INTERNAL_SYSCALL_DECL (err);
-  pd->pid = pd->tid = INTERNAL_SYSCALL (set_tid_address, err, 1, &pd->tid);
-#endif
+  __pthread_initialize_pids (pd);
   THREAD_SETMEM (pd, specific[0], &pd->specific_1stblock[0]);
   THREAD_SETMEM (pd, user_stack, true);
   if (LLL_LOCK_INITIALIZER != 0)
diff --git a/nptl/pthread-pids.h b/nptl/pthread-pids.h
new file mode 100644
index 0000000..33d764c
--- /dev/null
+++ b/nptl/pthread-pids.h
@@ -0,0 +1,29 @@
+/* Initialize pid and tid fields of struct pthread.  Stub version.
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library 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.
+
+   The GNU C Library 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 the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <pthreadP.h>
+
+/* Initialize PD->pid and PD->tid for the initial thread.  If there is
+   setup required to arrange that __exit_thread causes PD->tid to be
+   cleared and futex-woken, then this function should do that as well.  */
+static inline void
+__pthread_initialize_pids (struct pthread *pd)
+{
+#error "sysdeps pthread-pids.h file required"
+  pd->pid = pd->tid = -1;
+}
diff --git a/sysdeps/nacl/createthread.c b/sysdeps/nacl/createthread.c
index 9df4eae..9d9284a 100644
--- a/sysdeps/nacl/createthread.c
+++ b/sysdeps/nacl/createthread.c
@@ -17,6 +17,7 @@
    <http://www.gnu.org/licenses/>.  */
 
 #include <nacl-interfaces.h>
+#include <pthread-pids.h>
 
 /* See the comments in pthread_create.c for the requirements for these
    two macros and the create_thread function.  */
@@ -33,6 +34,8 @@ static int
 create_thread (struct pthread *pd, const struct pthread_attr *attr,
 	       bool stopped_start, STACK_VARIABLES_PARMS, bool *thread_ran)
 {
+  pd->tid = __nacl_get_tid (pd);
+
   pd->stopped_start = stopped_start;
   if (__glibc_unlikely (stopped_start))
     /* We make sure the thread does not run far by forcing it to get a
diff --git a/sysdeps/nacl/pthread-pids.h b/sysdeps/nacl/pthread-pids.h
new file mode 100644
index 0000000..ccb99d6
--- /dev/null
+++ b/sysdeps/nacl/pthread-pids.h
@@ -0,0 +1,65 @@
+/* Initialize pid and tid fields of struct pthread.  NaCl version.
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library 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.
+
+   The GNU C Library 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 the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <pthreadP.h>
+
+
+/* NaCl has no concept of PID or TID, nor even any notion of an
+   identifier for a thread within the process.  But various places in
+   the NPTL implementation rely on using the 'tid' field of the TCB
+   (struct pthread) as an identifier that is unique at least among all
+   live threads in the process.  So we must synthesize some number to
+   use.  Conveniently, the 'pthread_t' value itself is already unique
+   in exactly this way (because it's the 'struct pthread' pointer).
+
+   The only wrinkle is that 'tid' is a (32-bit) 'int' and its high
+   (sign) bit is used for special purposes, so we must be absolutely
+   sure that we never use a pointer value with the high bit set.  (It
+   also cannot be zero, but zero is never a valid pointer anyway.)
+   The NaCl sandbox models for 32-bit machines limit the address space
+   to less than 3GB (in fact, to 1GB), so it's already impossible that
+   a valid pointer will have its high bit set.  But the NaCl x86-64
+   sandbox model allows a full 4GB of address space, so we cannot
+   assume that an arbitrary pointer value will not have the high bit
+   set.  Conveniently, there are always unused bits in the pointer
+   value for a 'struct pthread', because it is always aligned to at
+   least 32 bits and so the low bits are always zero.  Hence, we can
+   safely avoid the danger of a nonzero high bit just by shifting the
+   pointer value right.  */
+
+static inline int
+__nacl_get_tid (struct pthread *pd)
+{
+  uintptr_t id = (uintptr_t) pd;
+  int tid = id >> 1;
+  assert ((id & 1) == 0);
+  assert (sizeof id == sizeof tid);
+  assert (tid > 0);
+  return tid;
+}
+
+
+/* Initialize PD->pid and PD->tid for the initial thread.  If there is
+   setup required to arrange that __exit_thread causes PD->tid to be
+   cleared and futex-woken, then this function should do that as well.  */
+static inline void
+__pthread_initialize_pids (struct pthread *pd)
+{
+  pd->tid = __nacl_get_tid (pd);
+  pd->pid = -1;
+}
diff --git a/sysdeps/unix/sysv/linux/pthread-pids.h b/sysdeps/unix/sysv/linux/pthread-pids.h
new file mode 100644
index 0000000..d333648
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/pthread-pids.h
@@ -0,0 +1,30 @@
+/* Initialize pid and tid fields of struct pthread.  Linux version.
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library 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.
+
+   The GNU C Library 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 the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <pthreadP.h>
+#include <sysdep.h>
+
+/* Initialize PD->pid and PD->tid for the initial thread.  If there is
+   setup required to arrange that __exit_thread causes PD->tid to be
+   cleared and futex-woken, then this function should do that as well.  */
+static inline void
+__pthread_initialize_pids (struct pthread *pd)
+{
+  INTERNAL_SYSCALL_DECL (err);
+  pd->pid = pd->tid = INTERNAL_SYSCALL (set_tid_address, err, 1, &pd->tid);
+}
