diff --git a/doc/changelog.txt b/doc/changelog.txt
index 190c9c8a..de892905 100644
--- a/doc/changelog.txt
+++ b/doc/changelog.txt
@@ -2,6 +2,7 @@
 
 Fixes:
 - ftp: Fix support for FTP ports other than the default.
+- build: Use _WIN32 instead of WIN32 define to detect Windows systems.
 
 Changes:
 - checking: Caches are now size-restricted to limit the memory
diff --git a/linkcheck/network/_network.c b/linkcheck/network/_network.c
index f2be36f2..d667d5a6 100644
--- a/linkcheck/network/_network.c
+++ b/linkcheck/network/_network.c
@@ -16,7 +16,7 @@
 */
 
 #include "Python.h"
-#ifndef WIN32
+#ifndef _WIN32
 #include <sys/ioctl.h>
 #include <sys/socket.h>
 #include <net/route.h>
@@ -32,7 +32,7 @@ static PyObject* network_ifreq_size (PyObject* self, PyObject* args)
     if (!PyArg_ParseTuple(args, ""))
         return NULL;
     return Py_BuildValue("i", 
-#ifdef WIN32
+#ifdef _WIN32
 0
 #else
 sizeof(struct ifreq)