-- a/libcxx/include/thread
+++ b/libcxx/include/thread
@@ -370,7 +370,7 @@ sleep_for(const chrono::duration<_Rep, _Period>& __d)
     using namespace chrono;
     if (__d > duration<_Rep, _Period>::zero())
     {
-#if defined(_LIBCPP_COMPILER_GCC) && (__powerpc__ || __POWERPC__)
+#if ! (defined(_LIBCPP_COMPILER_GCC) && (__powerpc__ || __POWERPC__))
     //  GCC's long double const folding is incomplete for IBM128 long doubles.
         _LIBCPP_CONSTEXPR duration<long double> _Max = nanoseconds::max();
 #else