diff --git a/src/backend/file/gnc-backend-file.c b/src/backend/file/gnc-backend-file.c
index a673726a77..3857251ae2 100644
--- a/src/backend/file/gnc-backend-file.c
+++ b/src/backend/file/gnc-backend-file.c
@@ -83,7 +83,7 @@ static gboolean
 gnc_file_be_get_file_lock (FileBackend *be)
 {
     struct stat statbuf;
-#ifndef _WIN32
+#ifndef G_OS_WIN32
     char pathbuf[PATH_MAX];
     char *path = NULL;
 #endif
@@ -132,7 +132,7 @@ gnc_file_be_get_file_lock (FileBackend *be)
      * provides a better long-term solution.
      */
 
-#ifndef _WIN32
+#ifndef G_OS_WIN32
     strcpy (pathbuf, be->lockfile);
     path = strrchr (pathbuf, '.');
     sprintf (path, ".%lx.%d.LNK", gethostid(), getpid());
@@ -183,12 +183,12 @@ gnc_file_be_get_file_lock (FileBackend *be)
 
     return TRUE;
 
-#else /* ifndef _WIN32 */
+#else /* ifndef G_OS_WIN32 */
     /* On windows, there is no NFS and the open(,O_CREAT | O_EXCL)
        is sufficient for locking. */
     be->linkfile = NULL;
     return TRUE;
-#endif /* ifndef _WIN32 */
+#endif /* ifndef G_OS_WIN32 */
 }
 
 /* ================================================================= */
diff --git a/src/backend/file/io-gncxml-v2.c b/src/backend/file/io-gncxml-v2.c
index 646e6af328..597373e496 100644
--- a/src/backend/file/io-gncxml-v2.c
+++ b/src/backend/file/io-gncxml-v2.c
@@ -1239,7 +1239,7 @@ try_gz_open (const char *filename, const char *perms, gboolean use_gzip,
   if (!use_gzip)
     return fopen(filename, perms);
 
-#ifdef _WIN32
+#ifdef G_OS_WIN32
   PWARN("Compression not implemented on Windows. Opening uncompressed file.");
   return fopen(filename, perms);
 
diff --git a/src/gnome-utils/druid-gconf-setup.c b/src/gnome-utils/druid-gconf-setup.c
index 276f266c57..5b58057156 100644
--- a/src/gnome-utils/druid-gconf-setup.c
+++ b/src/gnome-utils/druid-gconf-setup.c
@@ -614,7 +614,7 @@ druid_gconf_install_check_schemas (void)
     return;
   }
 
-#ifdef _WIN32
+#ifdef G_OS_WIN32
   {
     /* automatically update the search path on windows */
     GError *error = NULL;
@@ -631,7 +631,7 @@ druid_gconf_install_check_schemas (void)
       return;
     }
   }
-#endif /* _WIN32 */
+#endif /* G_OS_WIN32 */
 
   xml = gnc_glade_xml_new ("druid-gconf-setup.glade", "GConf Query");
   dialog = glade_xml_get_widget (xml, "GConf Query");