diff --git a/glib/tests/date.c b/glib/tests/date.c
index 6239d510b..012e70713 100644
--- a/glib/tests/date.c
+++ b/glib/tests/date.c
@@ -379,7 +379,7 @@ main (int argc, char** argv)
     3000, 3001, 3002, 3998, 3999, 4000, 4001, 4002, 4003
   };
 
-  g_setenv ("LANG", "en_US.utf-8", TRUE);
+  g_setenv ("LC_ALL", "en_US.utf-8", TRUE);
   setlocale (LC_ALL, "");
 #ifdef G_OS_WIN32
   SetThreadLocale (MAKELCID (MAKELANGID (LANG_ENGLISH, SUBLANG_ENGLISH_US), SORT_DEFAULT));
diff --git a/glib/tests/fileutils.c b/glib/tests/fileutils.c
index 550c4d874..d218e78a0 100644
--- a/glib/tests/fileutils.c
+++ b/glib/tests/fileutils.c
@@ -905,6 +905,7 @@ int
 main (int   argc,
       char *argv[])
 {
+  g_setenv ("LC_ALL", "C", TRUE);
   g_test_init (&argc, &argv, NULL);
 
   g_test_add_func ("/fileutils/build-path", test_build_path);
diff --git a/glib/tests/markup-subparser.c b/glib/tests/markup-subparser.c
index 32188804d..13362664a 100644
--- a/glib/tests/markup-subparser.c
+++ b/glib/tests/markup-subparser.c
@@ -373,6 +373,7 @@ TestCase error_cases[] = /* error cases */
 int
 main (int argc, char **argv)
 {
+  g_setenv ("LC_ALL", "C", TRUE);
   g_test_init (&argc, &argv, NULL);
   add_tests (test, "/glib/markup/subparser/success", test_cases);
   add_tests (test, "/glib/markup/subparser/failure", error_cases);
diff --git a/glib/tests/option-context.c b/glib/tests/option-context.c
index cad40a08a..12b86229f 100644
--- a/glib/tests/option-context.c
+++ b/glib/tests/option-context.c
@@ -71,8 +71,6 @@ print_help (GOptionContext *options, gchar **argv)
   gint    argc = 3;
   GError *error = NULL;
 
-  g_setenv ("LANG", "C", TRUE);
-
   g_option_context_parse (options, &argc, &argv, &error);
   g_option_context_free (options);
   exit(0);
@@ -2487,6 +2485,7 @@ main (int   argc,
   int i;
   gchar *test_name;
 
+  g_setenv ("LC_ALL", "C", TRUE);
   g_test_init (&argc, &argv, NULL);
 
   g_test_bug_base ("http://bugzilla.gnome.org/");