diff --git a/libcxx/src/debug.cpp b/libcxx/src/debug.cpp
--- a/libcxx/src/debug.cpp
+++ b/libcxx/src/debug.cpp
@@ -14,7 +14,7 @@
 #include "cstdio"
 #include "__hash_table"
 #ifndef _LIBCPP_HAS_NO_THREADS
-#include "mutex"
+#include "__threading_support"
 #if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
 #pragma comment(lib, "pthread")
 #endif
@@ -62,17 +62,22 @@
 {
 
 #ifndef _LIBCPP_HAS_NO_THREADS
-typedef mutex mutex_type;
-typedef lock_guard<mutex_type> WLock;
-typedef lock_guard<mutex_type> RLock;
-
-mutex_type&
-mut()
-{
-    static _LIBCPP_NO_DESTROY mutex_type m;
-    return m;
-}
-#endif // !_LIBCPP_HAS_NO_THREADS
+_LIBCPP_SAFE_STATIC static __libcpp_mutex_t __db_mut = _LIBCPP_MUTEX_INITIALIZER;
+
+struct db_guard {
+  bool owns_lock = true;
+  db_guard() { __libcpp_mutex_lock(&__db_mut); }
+  ~db_guard() {
+    if (owns_lock)
+      __libcpp_mutex_unlock(&__db_mut);
+  }
+  void release() { owns_lock = false; }
+};
+#else
+struct db_guard {
+  void release() {};
+};
+#endif
 
 }  // unnamed namespace
 
@@ -136,9 +141,8 @@
 void*
 __libcpp_db::__find_c_from_i(void* __i) const
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    RLock _(mut());
-#endif
+    // Read lock
+    db_guard lk;
     __i_node* i = __find_iterator(__i);
     _LIBCPP_ASSERT(i != nullptr, "iterator not found in debug database.");
     return i->__c_ != nullptr ? i->__c_->__c_ : nullptr;
@@ -147,9 +151,8 @@
 void
 __libcpp_db::__insert_ic(void* __i, const void* __c)
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    WLock _(mut());
-#endif
+    // Write lock
+    db_guard lk;
     if (__cbeg_ == __cend_)
         return;
     size_t hc = hash<const void*>()(__c) % static_cast<size_t>(__cend_ - __cbeg_);
@@ -170,9 +173,8 @@
 void
 __libcpp_db::__insert_c(void* __c, __libcpp_db::_InsertConstruct *__fn)
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    WLock _(mut());
-#endif
+    // Write lock
+    db_guard lk;
     if (__csz_ + 1 > static_cast<size_t>(__cend_ - __cbeg_))
     {
         size_t nc = __next_prime(2*static_cast<size_t>(__cend_ - __cbeg_) + 1);
@@ -209,9 +211,8 @@
 void
 __libcpp_db::__erase_i(void* __i)
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    WLock _(mut());
-#endif
+    // Write lock
+    db_guard lk;
     if (__ibeg_ != __iend_)
     {
         size_t hi = hash<void*>()(__i) % static_cast<size_t>(__iend_ - __ibeg_);
@@ -242,9 +243,8 @@
 void
 __libcpp_db::__invalidate_all(void* __c)
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    WLock _(mut());
-#endif
+    // Write lock
+    db_guard lk;
     if (__cend_ != __cbeg_)
     {
         size_t hc = hash<void*>()(__c) % static_cast<size_t>(__cend_ - __cbeg_);
@@ -268,36 +268,23 @@
 __c_node*
 __libcpp_db::__find_c_and_lock(void* __c) const
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    mut().lock();
-#endif
+    // Write lock - caller is likely to perform a write operation
+    db_guard lk;
     if (__cend_ == __cbeg_)
-    {
-#ifndef _LIBCPP_HAS_NO_THREADS
-        mut().unlock();
-#endif
         return nullptr;
-    }
+
     size_t hc = hash<void*>()(__c) % static_cast<size_t>(__cend_ - __cbeg_);
     __c_node* p = __cbeg_[hc];
     if (p == nullptr)
-    {
-#ifndef _LIBCPP_HAS_NO_THREADS
-        mut().unlock();
-#endif
         return nullptr;
-    }
+
     while (p->__c_ != __c)
     {
         p = p->__next_;
         if (p == nullptr)
-        {
-#ifndef _LIBCPP_HAS_NO_THREADS
-            mut().unlock();
-#endif
             return nullptr;
-        }
     }
+    lk.release();
     return p;
 }
 
@@ -319,16 +306,15 @@
 __libcpp_db::unlock() const
 {
 #ifndef _LIBCPP_HAS_NO_THREADS
-    mut().unlock();
+    __libcpp_mutex_unlock(&__db_mut);
 #endif
 }
 
 void
 __libcpp_db::__erase_c(void* __c)
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    WLock _(mut());
-#endif
+    // Write lock
+    db_guard lk;
     if (__cend_ != __cbeg_)
     {
         size_t hc = hash<void*>()(__c) % static_cast<size_t>(__cend_ - __cbeg_);
@@ -363,9 +349,8 @@
 void
 __libcpp_db::__iterator_copy(void* __i, const void* __i0)
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    WLock _(mut());
-#endif
+    // Write lock
+    db_guard lk;
     __i_node* i = __find_iterator(__i);
     __i_node* i0 = __find_iterator(__i0);
     __c_node* c0 = i0 != nullptr ? i0->__c_ : nullptr;
@@ -391,9 +376,8 @@
 bool
 __libcpp_db::__dereferenceable(const void* __i) const
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    RLock _(mut());
-#endif
+    // Read lock
+    db_guard lk;
     __i_node* i = __find_iterator(__i);
     return i != nullptr && i->__c_ != nullptr && i->__c_->__dereferenceable(__i);
 }
@@ -401,9 +385,8 @@
 bool
 __libcpp_db::__decrementable(const void* __i) const
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    RLock _(mut());
-#endif
+    // Read lock
+    db_guard lk;
     __i_node* i = __find_iterator(__i);
     return i != nullptr && i->__c_ != nullptr && i->__c_->__decrementable(__i);
 }
@@ -411,9 +394,8 @@
 bool
 __libcpp_db::__addable(const void* __i, ptrdiff_t __n) const
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    RLock _(mut());
-#endif
+    // Read lock
+    db_guard lk;
     __i_node* i = __find_iterator(__i);
     return i != nullptr && i->__c_ != nullptr && i->__c_->__addable(__i, __n);
 }
@@ -421,9 +403,8 @@
 bool
 __libcpp_db::__subscriptable(const void* __i, ptrdiff_t __n) const
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    RLock _(mut());
-#endif
+    // Read lock
+    db_guard lk;
     __i_node* i = __find_iterator(__i);
     return i != nullptr && i->__c_ != nullptr && i->__c_->__subscriptable(__i, __n);
 }
@@ -431,9 +412,8 @@
 bool
 __libcpp_db::__less_than_comparable(const void* __i, const void* __j) const
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    RLock _(mut());
-#endif
+    // Read lock
+    db_guard lk;
     __i_node* i = __find_iterator(__i);
     __i_node* j = __find_iterator(__j);
     __c_node* ci = i != nullptr ? i->__c_ : nullptr;
@@ -444,9 +424,8 @@
 void
 __libcpp_db::swap(void* c1, void* c2)
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    WLock _(mut());
-#endif
+    // Write lock
+    db_guard lk;
     size_t hc = hash<void*>()(c1) % static_cast<size_t>(__cend_ - __cbeg_);
     __c_node* p1 = __cbeg_[hc];
     _LIBCPP_ASSERT(p1 != nullptr, "debug mode internal logic error swap A");
@@ -475,9 +454,8 @@
 void
 __libcpp_db::__insert_i(void* __i)
 {
-#ifndef _LIBCPP_HAS_NO_THREADS
-    WLock _(mut());
-#endif
+    // Write lock
+    db_guard lk;
     __insert_iterator(__i);
 }