diff --git a/include/rapidjson/internal/biginteger.h b/include/rapidjson/internal/biginteger.h
old mode 100644
new mode 100755
index 06a442b..72acfc3
--- a/include/rapidjson/internal/biginteger.h
+++ b/include/rapidjson/internal/biginteger.h
@@ -23,6 +23,10 @@
 
 #include "../rapidjson.h"
 
+#if defined(_MSC_VER) && defined(_M_AMD64)
+#include <intrin.h> // for _umul128
+#endif
+
 RAPIDJSON_NAMESPACE_BEGIN
 namespace internal {