diff --git a/include/__memory/shared_ptr.h b/include/__memory/shared_ptr.h
index d9ddb8a..4b9da00 100644
--- a/include/__memory/shared_ptr.h
+++ b/include/__memory/shared_ptr.h
@@ -54,7 +54,7 @@
 #include <stdexcept>
 #include <typeinfo>
 #if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
-#  include <__atomic/memory_order.h>
+#  include <atomic>
 #endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -149,7 +149,12 @@ class _LIBCPP_EXPORTED_FROM_ABI __shared_count
     __shared_count& operator=(const __shared_count&);
 
 protected:
-    long __shared_owners_;
+#ifdef _LIBCPP_HAS_NO_THREADS
+    typedef long __atomic_count;
+#else
+    typedef atomic<long> __atomic_count;
+#endif
+    __atomic_count __shared_owners_;
     virtual ~__shared_count();
 private:
     virtual void __on_zero_shared() _NOEXCEPT = 0;
@@ -165,11 +170,19 @@ public:
 #else
     _LIBCPP_INLINE_VISIBILITY
     void __add_shared() _NOEXCEPT {
+#ifdef _LIBCPP_HAS_NO_THREADS
       __libcpp_atomic_refcount_increment(__shared_owners_);
+#else
+      __shared_owners_++;
+#endif
     }
     _LIBCPP_INLINE_VISIBILITY
     bool __release_shared() _NOEXCEPT {
+#ifdef _LIBCPP_HAS_NO_THREADS
       if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) {
+#else
+      if (--__shared_owners_ == -1) {
+#endif
         __on_zero_shared();
         return true;
       }
@@ -178,14 +191,23 @@ public:
 #endif
     _LIBCPP_INLINE_VISIBILITY
     long use_count() const _NOEXCEPT {
+#ifdef _LIBCPP_HAS_NO_THREADS
         return __libcpp_relaxed_load(&__shared_owners_) + 1;
+#else
+        return __shared_owners_.load(memory_order_relaxed) + 1;
+#endif
     }
 };
 
 class _LIBCPP_EXPORTED_FROM_ABI __shared_weak_count
     : private __shared_count
 {
-    long __shared_weak_owners_;
+#ifdef _LIBCPP_HAS_NO_THREADS
+    typedef long __atomic_count;
+#else
+    typedef atomic<long> __atomic_count;
+#endif
+    __atomic_count __shared_weak_owners_;
 
 public:
     _LIBCPP_INLINE_VISIBILITY
@@ -207,7 +229,11 @@ public:
     }
     _LIBCPP_INLINE_VISIBILITY
     void __add_weak() _NOEXCEPT {
+#ifdef _LIBCPP_HAS_NO_THREADS
       __libcpp_atomic_refcount_increment(__shared_weak_owners_);
+#else
+      __shared_weak_owners_++;
+#endif
     }
     _LIBCPP_INLINE_VISIBILITY
     void __release_shared() _NOEXCEPT {