diff --git a/newlib/libc/include/sys/lock.h b/newlib/libc/include/sys/lock.h
index 9075e35c9179968031010432515e3a845ff6ca8d..a406ec7fd71f10b81bdfb0ca2476fa5ea50e0c0b 100644
--- a/newlib/libc/include/sys/lock.h
+++ b/newlib/libc/include/sys/lock.h
@@ -8,8 +8,14 @@ typedef int _LOCK_RECURSIVE_T;
  
 #include <_ansi.h>
 
+#ifdef __SINGLE_THREAD__
+#define __LOCK_INIT(class,lock) ;
+#define __LOCK_INIT_RECURSIVE(class,lock) ;
+#else
 #define __LOCK_INIT(class,lock) static int lock = 0;
 #define __LOCK_INIT_RECURSIVE(class,lock) static int lock = 0;
+#endif
+
 #define __lock_init(lock) (_CAST_VOID 0)
 #define __lock_init_recursive(lock) (_CAST_VOID 0)
 #define __lock_close(lock) (_CAST_VOID 0)
diff --git a/newlib/libc/posix/telldir.c b/newlib/libc/posix/telldir.c
index 0a8eac024b4955cd70b192307938358bb1cb2236..959e3b7bb78860f775e0de2f9d52ff2eb6b67411 100644
--- a/newlib/libc/posix/telldir.c
+++ b/newlib/libc/posix/telldir.c
@@ -70,7 +70,7 @@ struct ddloc {
 static long	dd_loccnt = 1;	/* Index of entry for sequential readdir's */
 static struct	ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
 
-#ifdef HAVE_DD_LOCK
+#if !defined(__SINGLE_THREAD__) && defined(HAVE_DD_LOCK)
 __LOCK_INIT(static, __dd_hash_mutex);
 #endif
 
@@ -92,8 +92,10 @@ _DEFUN(telldir, (dirp),
 
 #ifdef HAVE_DD_LOCK
 	__lock_acquire_recursive(dirp->dd_lock);
+#ifndef __SINGLE_THREAD__
 	__lock_acquire(__dd_hash_mutex);
 #endif
+#endif
 	index = dd_loccnt++;
 	lp->loc_index = index;
 	lp->loc_seek = dirp->dd_seek;
@@ -102,7 +104,9 @@ _DEFUN(telldir, (dirp),
 	lp->loc_next = dd_hash[LOCHASH(index)];
 	dd_hash[LOCHASH(index)] = lp;
 #ifdef HAVE_DD_LOCK
+#ifndef __SINGLE_THREAD__
 	__lock_release(__dd_hash_mutex);
+#endif
 	__lock_release_recursive(dirp->dd_lock);
 #endif
 	return (index);
@@ -123,7 +127,7 @@ _DEFUN(_seekdir, (dirp, loc),
 	register struct ddloc **prevlp;
 	struct dirent *dp;
 
-#ifdef HAVE_DD_LOCK
+#if !defined(__SINGLE_THREAD__) && defined(HAVE_DD_LOCK)
 	__lock_acquire(__dd_hash_mutex);
 #endif
 	if (loc != 0) {
@@ -136,7 +140,7 @@ _DEFUN(_seekdir, (dirp, loc),
 			lp = lp->loc_next;
 		}
 		if (lp == NULL) {
-#ifdef HAVE_DD_LOCK
+#if !defined(__SINGLE_THREAD__) && defined(HAVE_DD_LOCK)
 			__lock_release(__dd_hash_mutex);
 #endif
 			return;
@@ -162,7 +166,7 @@ found:
 		dirp->dd_seek = 0;
 		dirp->dd_loc = 0;
 	}
-#ifdef HAVE_DD_LOCK
+#if !defined(__SINGLE_THREAD__) && defined(HAVE_DD_LOCK)
 	__lock_release(__dd_hash_mutex);
 #endif
 }
@@ -174,7 +178,7 @@ _DEFUN(_cleanupdir, (dirp),
 {
 	int i;
 
-#ifdef HAVE_DD_LOCK
+#if !defined(__SINGLE_THREAD__) && defined(HAVE_DD_LOCK)
 	__lock_acquire(__dd_hash_mutex);
 #endif
 	for (i = 0; i < NDIRHASH; ++i) {
@@ -199,7 +203,7 @@ _DEFUN(_cleanupdir, (dirp),
 		}
 		dd_hash[i] = head.loc_next;
 	}
-#ifdef HAVE_DD_LOCK
+#if !defined(__SINGLE_THREAD__) && defined(HAVE_DD_LOCK)
 	__lock_release(__dd_hash_mutex);
 #endif
 
diff --git a/newlib/libc/stdlib/__call_atexit.c b/newlib/libc/stdlib/__call_atexit.c
index 7d5e0d0464b4b9ff74fcb003d965a3c2da020699..6a809cc4d5bd09905d010fdc21708a537166971d 100644
--- a/newlib/libc/stdlib/__call_atexit.c
+++ b/newlib/libc/stdlib/__call_atexit.c
@@ -11,7 +11,9 @@
 /* Make this a weak reference to avoid pulling in free.  */
 void free(void *) _ATTRIBUTE((__weak__));
 
+#ifndef __SINGLE_THREAD__
 __LOCK_INIT_RECURSIVE(, __atexit_recursive_mutex);
+#endif
 
 #ifdef _REENT_GLOBAL_ATEXIT
 struct _atexit *_global_atexit = _NULL;
diff --git a/newlib/libc/stdlib/arc4random.h b/newlib/libc/stdlib/arc4random.h
index 3c5fe235338270b1af48190cefa9278ea3af917f..4b9855305f5cbce00dd96ee58ed32d1ad48aa5cf 100644
--- a/newlib/libc/stdlib/arc4random.h
+++ b/newlib/libc/stdlib/arc4random.h
@@ -47,7 +47,9 @@
 
 #endif /* _ARC4_LOCK_INIT */
 
+#ifndef __SINGLE_THREAD__
 _ARC4_LOCK_INIT
+#endif
 
 #ifdef _ARC4RANDOM_DATA
 _ARC4RANDOM_DATA
diff --git a/newlib/libc/stdlib/arc4random.c b/newlib/libc/stdlib/arc4random.c
index 75cdff3bc4b5d4245cce4130df64aebc956c853f..3cccc3ed46a5e9e756d4e216cb7686589eb60993 100644
--- a/newlib/libc/stdlib/arc4random.c
+++ b/newlib/libc/stdlib/arc4random.c
@@ -180,16 +180,24 @@ arc4random(void)
 {
 	uint32_t val;
 
+#ifndef __SINGLE_THREAD__
 	_ARC4_LOCK();
+#endif
 	_rs_random_u32(&val);
+#ifndef __SINGLE_THREAD__
 	_ARC4_UNLOCK();
+#endif
 	return val;
 }
 
 void
 arc4random_buf(void *buf, size_t n)
 {
+#ifndef __SINGLE_THREAD__
 	_ARC4_LOCK();
+#endif
 	_rs_random_buf(buf, n);
+#ifndef __SINGLE_THREAD__
 	_ARC4_UNLOCK();
+#endif
 }
diff --git a/newlib/libc/stdlib/quick_exit.c b/newlib/libc/stdlib/quick_exit.c
index aaa5f9f7f1df12dace7d87271291aa87cd2fb3b1..5ab2609bf04d508a228049a52aea5e6ec7216d54 100644
--- a/newlib/libc/stdlib/quick_exit.c
+++ b/newlib/libc/stdlib/quick_exit.c
@@ -44,7 +44,9 @@ struct quick_exit_handler {
 /**
  * Lock protecting the handlers list.
  */
+#ifndef __SINGLE_THREAD__
 __LOCK_INIT(static, __at_quick_exit_mutex);
+#endif
 /**
  * Stack of cleanup handlers.  These will be invoked in reverse order when
  */
@@ -60,10 +62,14 @@ at_quick_exit(void (*func)(void))
 	if (NULL == h)
 		return (1);
 	h->cleanup = func;
+#ifndef __SINGLE_THREAD__
 	__lock_acquire(__at_quick_exit_mutex);
+#endif
 	h->next = handlers;
 	handlers = h;
+#ifndef __SINGLE_THREAD__
 	__lock_release(__at_quick_exit_mutex);
+#endif
 	return (0);
 }