diff --git a/wagtail_modeltranslation/apps.py b/wagtail_modeltranslation/apps.py
index f77efc0..a21d273 100644
--- a/wagtail_modeltranslation/apps.py
+++ b/wagtail_modeltranslation/apps.py
@@ -10,9 +10,22 @@ class ModeltranslationConfig(AppConfig):
 
     def ready(self):
         from django.conf import settings
+        from modeltranslation import settings as mt_settings
+
         # Add Wagtail defined fields as modeltranslation custom fields
-        setattr(settings, 'MODELTRANSLATION_CUSTOM_FIELDS', getattr(settings, 'MODELTRANSLATION_CUSTOM_FIELDS', ()) + (
-            'StreamField', 'RichTextField'))
+        wagtail_fields = (
+            'StreamField',
+            'RichTextField',
+        )
+
+        # update both the standard settings and the modeltranslation settings,
+        # as we cannot guarantee the load order, and so django_modeltranslation
+        # may bootstrap itself either before, or after, our ready() gets called.
+        custom_fields = getattr(settings, 'MODELTRANSLATION_CUSTOM_FIELDS', tuple())
+        setattr(settings, 'MODELTRANSLATION_CUSTOM_FIELDS', tuple(set(custom_fields + wagtail_fields)))
+
+        mt_custom_fields = getattr(mt_settings, 'CUSTOM_FIELDS', tuple())
+        setattr(mt_settings, 'CUSTOM_FIELDS', tuple(set(mt_custom_fields + wagtail_fields)))
 
         from modeltranslation.models import handle_translation_registrations
         handle_translation_registrations()