diff --git a/libcxx/include/__config b/include/__config
--- a/libcxx/include/__config
+++ b/include/__config
@@ -1083,7 +1083,7 @@
 #  elif defined(_LIBCPP_WIN32API)
 #    define _LIBCPP_HAS_THREAD_API_WIN32
 #  else
-#    error "No thread API"
+#    define _LIBCPP_HAS_NO_THREADS
 #  endif // _LIBCPP_HAS_THREAD_API
 #endif // _LIBCPP_HAS_NO_THREADS