diff --git a/xbyak/xbyak.h b/xbyak/xbyak.h
index ed7706a..51b520d 100644
--- a/xbyak/xbyak.h
+++ b/xbyak/xbyak.h
@@ -37,6 +37,7 @@
 	#define XBYAK_GNUC_PREREQ(major, minor) 0
 #endif
 
+#if !defined(XBYAK_STD_UNORDERED_SET)
 // This covers -std=(gnu|c)++(0x|11|1y), -stdlib=libc++, and modern Microsoft.
 #if ((defined(_MSC_VER) && (_MSC_VER >= 1600)) || defined(_LIBCPP_VERSION) ||\
 	 			 ((__cplusplus >= 201103) || defined(__GXX_EXPERIMENTAL_CXX0X__)))
@@ -71,6 +72,8 @@
 	#define XBYAK_STD_UNORDERED_MAP std::map
 	#define XBYAK_STD_UNORDERED_MULTIMAP std::multimap
 #endif
+#endif
+
 #ifdef _WIN32
 	#ifndef WIN32_LEAN_AND_MEAN
 		#define WIN32_LEAN_AND_MEAN