diff --git a/gio/tests/gapplication.c b/gio/tests/gapplication.c
index 336135cb4..f5491ec9e 100644
--- a/gio/tests/gapplication.c
+++ b/gio/tests/gapplication.c
@@ -972,6 +972,8 @@ test_api (void)
 int
 main (int argc, char **argv)
 {
+  g_setenv ("LC_ALL", "C", TRUE);
+
   g_test_init (&argc, &argv, NULL);
 
   g_test_dbus_unset ();
diff --git a/gio/tests/gdbus-serialization.c b/gio/tests/gdbus-serialization.c
index da28f1bc1..d2f0a6ce7 100644
--- a/gio/tests/gdbus-serialization.c
+++ b/gio/tests/gdbus-serialization.c
@@ -1085,6 +1085,7 @@ int
 main (int   argc,
       char *argv[])
 {
+  g_setenv ("LC_ALL", "C", TRUE);
   setlocale (LC_ALL, "C");
 
   g_test_init (&argc, &argv, NULL);
diff --git a/gio/tests/gsettings.c b/gio/tests/gsettings.c
index 2f056ee95..ba80647f1 100644
--- a/gio/tests/gsettings.c
+++ b/gio/tests/gsettings.c
@@ -741,15 +741,18 @@ test_l10n (void)
 
   settings = g_settings_new ("org.gtk.test.localized");
 
+  g_setenv ("LC_MESSAGES", "C", TRUE);
   setlocale (LC_MESSAGES, "C");
   str = g_settings_get_string (settings, "error-message");
+  g_setenv ("LC_MESSAGES", locale, TRUE);
   setlocale (LC_MESSAGES, locale);
 
   g_assert_cmpstr (str, ==, "Unnamed");
   g_free (str);
   str = NULL;
 
-  setlocale (LC_MESSAGES, "de_DE");
+  g_setenv ("LC_MESSAGES", "de_DE.UTF-8", TRUE);
+  setlocale (LC_MESSAGES, "de_DE.UTF-8");
   /* Only do the test if translation is actually working... */
   if (g_str_equal (dgettext ("test", "\"Unnamed\""), "\"Unbenannt\""))
     {
@@ -762,6 +765,7 @@ test_l10n (void)
   else
     g_printerr ("warning: translation is not working... skipping test. ");
 
+  g_setenv ("LC_MESSAGES", locale, TRUE);
   setlocale (LC_MESSAGES, locale);
   g_free (locale);
   g_object_unref (settings);
@@ -788,15 +792,18 @@ test_l10n_context (void)
 
   settings = g_settings_new ("org.gtk.test.localized");
 
+  g_setenv ("LC_MESSAGES", "C", TRUE);
   setlocale (LC_MESSAGES, "C");
   g_settings_get (settings, "backspace", "s", &str);
+  g_setenv ("LC_MESSAGES", locale, TRUE);
   setlocale (LC_MESSAGES, locale);
 
   g_assert_cmpstr (str, ==, "BackSpace");
   g_free (str);
   str = NULL;
 
-  setlocale (LC_MESSAGES, "de_DE");
+  g_setenv ("LC_MESSAGES", "de_DE.UTF-8", TRUE);
+  setlocale (LC_MESSAGES, "de_DE.UTF-8");
   /* Only do the test if translation is actually working... */
   if (g_str_equal (dgettext ("test", "\"Unnamed\""), "\"Unbenannt\""))
     {
@@ -809,6 +816,7 @@ test_l10n_context (void)
   else
     g_printerr ("warning: translation is not working... skipping test.  ");
 
+  g_setenv ("LC_MESSAGES", locale, TRUE);
   setlocale (LC_MESSAGES, locale);
   g_free (locale);
   g_object_unref (settings);