diff --git a/win32/Make.rules.mak b/win32/Make.rules.mak
index 94514984..cf05da26 100644
--- a/win32/Make.rules.mak
+++ b/win32/Make.rules.mak
@@ -1,4 +1,4 @@
-COPTS = /Zi /ML /nologo /DHAVE_CONFIG_H /DVERSION=\"0.7.0\" /I$(TOPDIR)\src\include 
+COPTS = /Zi /ML /nologo /DHAVE_CONFIG_H /DVERSION=\"0.7.0\" /I$(TOPDIR)\src\include /D_WIN32_WINNT=0x0400
 LINKFLAGS = /DEBUG /NOLOGO /INCREMENTAL:NO /MACHINE:IX86