diff --git a/src_concurrent/piconditionvar.cpp b/src_concurrent/piconditionvar.cpp
index a52558e9..be9caa4a 100644
--- a/src_concurrent/piconditionvar.cpp
+++ b/src_concurrent/piconditionvar.cpp
@@ -4,6 +4,7 @@
 #include "pitime.h"
 
 #ifdef WINDOWS
+#undef _WIN32_WINNT
 #define _WIN32_WINNT 0x0600
 #include "synchapi.h"
 #include <windef.h>