diff --git a/lib/System/Threading.cpp b/lib/System/Threading.cpp
index c6a8214..bc41afe 100644
--- a/lib/System/Threading.cpp
+++ b/lib/System/Threading.cpp
@@ -11,6 +11,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/Config/config.h"
 #include "llvm/System/Threading.h"
 #include "llvm/System/Atomic.h"
 #include "llvm/System/Mutex.h"