diff --git a/src/util.h b/src/util.h
index bf4bdb63..32d407a6 100755
--- a/src/util.h
+++ b/src/util.h
@@ -47,6 +47,7 @@
 using namespace std; // because of the library: "vector"
 #ifdef _WIN32
 # include <winsock2.h>
+# include <ws2ipdef.h>
 # include <windows.h>
 # include <mmsystem.h>
 #elif defined ( __APPLE__ ) || defined ( __MACOSX )