diff --git a/gio/tests/contenttype.c b/gio/tests/contenttype.c
index 10b795a05..cb10c86c0 100644
--- a/gio/tests/contenttype.c
+++ b/gio/tests/contenttype.c
@@ -30,7 +30,7 @@ test_guess (void)
   existing_directory = (gchar *) g_getenv ("SYSTEMROOT");
 
   if (existing_directory)
-    existing_directory = g_strdup_printf ("%s/", existing_directory);
+    existing_directory = g_strdup_printf ("%s" G_DIR_SEPARATOR_S, existing_directory);
 #else
   existing_directory = g_strdup ("/etc/");
 #endif