diff --git a/lib/config-win32.h b/lib/config-win32.h
index e498192f8bee8775fff660e362dae4976f9ec17d..cfbca9ca3866e11e036844184331b0649ca686d7 100644
--- a/lib/config-win32.h
+++ b/lib/config-win32.h
@@ -653,10 +653,10 @@
 #undef OS
 #if defined(_M_IX86) || defined(__i386__) /* x86 (MSVC or gcc) */
 #define OS "i386-pc-win32"
+#elif defined(_M_X64) || defined(__x86_64__) /* x86_64 (MSVC >=2005 or gcc) */
+#define OS "x86_64-pc-win32"
 #elif defined(_M_IA64) /* Itanium */
 #define OS "ia64-pc-win32"
-#elif defined(_M_X64) /* AMD64/EM64T - Not defined until MSVC 2005 */
-#define OS "amd64-pc-win32"
 #else
 #define OS "unknown-pc-win32"
 #endif