diff --git a/src/include/refstring.h b/src/include/refstring.h
index 7845224..72daaef 100644
--- a/src/include/refstring.h
+++ b/src/include/refstring.h
@@ -9,12 +9,18 @@
 #ifndef _LIBCPP_REFSTRING_H
 #define _LIBCPP_REFSTRING_H
 
-#include "atomic_support.h"
 #include <__config>
 #include <cstddef>
 #include <cstring>
 #include <stdexcept>
 
+#if !defined(_LIBCPP_HAS_NO_THREADS) && !defined(_LIBCPP_CXX03_LANG) && !defined(_LIBCPP_USE_ATOMIC)
+#  define _LIBCPP_USE_ATOMIC
+#  include <atomic>
+#else
+#  include "atomic_support.h"
+#endif
+
 // MacOS and iOS used to ship with libstdc++, and still support old applications
 // linking against libstdc++. The libc++ and libstdc++ exceptions are supposed
 // to be ABI compatible, such that they can be thrown from one library and caught
@@ -40,7 +46,11 @@ typedef int count_t;
 struct _Rep_base {
   std::size_t len;
   std::size_t cap;
+#ifdef _LIBCPP_USE_ATOMIC
+  std::atomic<count_t> count;
+#else
   count_t count;
+#endif
 };
 
 inline _Rep_base* rep_from_data(const char* data_) noexcept {
@@ -88,7 +98,11 @@ inline __libcpp_refstring::__libcpp_refstring(const char* msg) {
 
 inline __libcpp_refstring::__libcpp_refstring(const __libcpp_refstring& s) noexcept : __imp_(s.__imp_) {
   if (__uses_refcount())
+#ifdef _LIBCPP_USE_ATOMIC
+    rep_from_data(__imp_)->count.fetch_add(1);
+#else
     __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
+#endif
 }
 
 inline __libcpp_refstring& __libcpp_refstring::operator=(__libcpp_refstring const& s) noexcept {
@@ -96,9 +110,19 @@ inline __libcpp_refstring& __libcpp_refstring::operator=(__libcpp_refstring cons
   struct _Rep_base* old_rep = rep_from_data(__imp_);
   __imp_                    = s.__imp_;
   if (__uses_refcount())
+#ifdef _LIBCPP_USE_ATOMIC
+    rep_from_data(__imp_)->count.fetch_add(1);
+#else
     __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
+#endif
+
   if (adjust_old_count) {
-    if (__libcpp_atomic_add(&old_rep->count, count_t(-1)) < 0) {
+#ifdef _LIBCPP_USE_ATOMIC
+    if (old_rep->count.fetch_sub(1) == 0)
+#else
+    if (__libcpp_atomic_add(&old_rep->count, count_t(-1)) < 0)
+#endif
+    {
       ::operator delete(old_rep);
     }
   }
@@ -108,7 +132,11 @@ inline __libcpp_refstring& __libcpp_refstring::operator=(__libcpp_refstring cons
 inline __libcpp_refstring::~__libcpp_refstring() {
   if (__uses_refcount()) {
     _Rep_base* rep = rep_from_data(__imp_);
+#ifdef _LIBCPP_USE_ATOMIC
+    if (rep->count.fetch_sub(1) == 0) {
+#else
     if (__libcpp_atomic_add(&rep->count, count_t(-1)) < 0) {
+#endif
       ::operator delete(rep);
     }
   }