diff --git a/include/future b/include/future
index 7cd88cb7..83513fa6 100644
--- a/include/future
+++ b/include/future
@@ -374,7 +374,7 @@ template <class R, class Alloc> struct uses_allocator<packaged_task<R>, Alloc>;
 #pragma GCC system_header
 #endif
 
-#ifndef _LIBCPP_HAS_NO_THREADS
+#ifdef _LIBCPP_HAS_NO_THREADS
 #error <future> is not supported on this single threaded system
 #else // !_LIBCPP_HAS_NO_THREADS
 
diff --git a/include/ios b/include/ios
index 6d426079..ff79998b 100644
--- a/include/ios
+++ b/include/ios
@@ -216,7 +216,7 @@ storage-class-specifier const error_category& iostream_category() noexcept;
 #include <__locale>
 #include <system_error>
 
-#if __has_feature(cxx_atomic) && !_LIBCPP_HAS_NO_THREADS
+#if __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
 #include <atomic>     // for __xindex_
 #endif
 
@@ -367,7 +367,7 @@ private:
     int*            __index_;
     size_t          __event_size_;
     size_t          __event_cap_;
-#if __has_feature(cxx_atomic) && !_LIBCPP_HAS_NO_THREADS
+#if __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
     static atomic<int> __xindex_;
 #else
     static int      __xindex_;
diff --git a/src/ios.cpp b/src/ios.cpp
index 0bd500bf..06426c7b 100644
--- a/src/ios.cpp
+++ b/src/ios.cpp
@@ -148,7 +148,7 @@ ios_base::getloc() const
 }
 
 // xalloc
-#if __has_feature(cxx_atomic) && !_LIBCPP_HAS_NO_THREADS
+#if __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
 atomic<int> ios_base::__xindex_ = ATOMIC_VAR_INIT(0);
 #else
 int ios_base::__xindex_ = 0;
diff --git a/src/memory.cpp b/src/memory.cpp
index 31e823cf..c56d031a 100644
--- a/src/memory.cpp
+++ b/src/memory.cpp
@@ -121,7 +121,7 @@ __shared_weak_count::__get_deleter(const type_info&) const _NOEXCEPT
 
 #endif  // _LIBCPP_NO_RTTI
 
-#if __has_feature(cxx_atomic) && !_LIBCPP_HAS_NO_THREADS
+#if __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
 
 static const std::size_t __sp_mut_count = 16;
 static pthread_mutex_t mut_back_imp[__sp_mut_count] =