diff --git a/docs/releases/1.6.rst b/docs/releases/1.6.rst
index cf7823e6fd..64590cccf0 100644
--- a/docs/releases/1.6.rst
+++ b/docs/releases/1.6.rst
@@ -45,3 +45,30 @@ The ``choices`` field on the ``wagtailforms.models.AbstractFormField`` model has
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 The ``wagtailimages.Filter`` model has been removed, and replaced with a ``Filter`` class instead. This class can be imported from the same location as the model: ``wagtail.wagtailimages.models.Filter``. The ``Filter`` class has the same API as the ``Filter`` model did, with the exception that Model methods such as ``Filter.save()``, and ``Filter.objects.get()`` have been removed.
+
+``TagSearchable`` needs removing from custom image / document model migrations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The mixin class ``wagtail.wagtailadmin.taggable.TagSearchable``, used internally by image and document models, has been deprecated. If you are using custom image or document models in your project, the migration(s) which created them will contain frozen references to ``wagtail.wagtailadmin.taggable.TagSearchable``, which must now be removed. The line:
+
+.. code-block:: python
+
+    import wagtail.wagtailadmin.taggable
+
+should be replaced by:
+
+.. code-block:: python
+
+    import wagtail.wagtailsearch.index
+
+and the line:
+
+.. code-block:: python
+
+    bases=(models.Model, wagtail.wagtailadmin.taggable.TagSearchable),
+
+should be updated to:
+
+.. code-block:: python
+
+    bases=(models.Model, wagtail.wagtailsearch.index.Indexed),
diff --git a/wagtail/tests/testapp/migrations/0001_initial.py b/wagtail/tests/testapp/migrations/0001_initial.py
index 62f695e8bd..c43dbddcdf 100644
--- a/wagtail/tests/testapp/migrations/0001_initial.py
+++ b/wagtail/tests/testapp/migrations/0001_initial.py
@@ -9,11 +9,11 @@ import taggit.managers
 from django.conf import settings
 from django.db import migrations, models
 
-import wagtail.wagtailadmin.taggable
 import wagtail.wagtailcore.blocks
 import wagtail.wagtailcore.fields
 import wagtail.wagtailimages.blocks
 import wagtail.wagtailimages.models
+import wagtail.wagtailsearch.index
 
 
 class Migration(migrations.Migration):
@@ -145,7 +145,7 @@ class Migration(migrations.Migration):
             options={
                 'abstract': False,
             },
-            bases=(models.Model, wagtail.wagtailadmin.taggable.TagSearchable),
+            bases=(models.Model, wagtail.wagtailsearch.index.Indexed),
         ),
         migrations.CreateModel(
             name='CustomImageFilePath',
@@ -167,7 +167,7 @@ class Migration(migrations.Migration):
             options={
                 'abstract': False,
             },
-            bases=(models.Model, wagtail.wagtailadmin.taggable.TagSearchable),
+            bases=(models.Model, wagtail.wagtailsearch.index.Indexed),
         ),
         migrations.CreateModel(
             name='CustomManagerPage',
diff --git a/wagtail/wagtaildocs/migrations/0001_initial.py b/wagtail/wagtaildocs/migrations/0001_initial.py
index 62f3d76612..1ca2778202 100644
--- a/wagtail/wagtaildocs/migrations/0001_initial.py
+++ b/wagtail/wagtaildocs/migrations/0001_initial.py
@@ -5,7 +5,7 @@ import taggit.managers
 from django.conf import settings
 from django.db import migrations, models
 
-import wagtail.wagtailadmin.taggable
+import wagtail.wagtailsearch.index
 
 
 class Migration(migrations.Migration):
@@ -46,6 +46,6 @@ class Migration(migrations.Migration):
             ],
             options={
             },
-            bases=(models.Model, wagtail.wagtailadmin.taggable.TagSearchable),
+            bases=(models.Model, wagtail.wagtailsearch.index.Indexed),
         ),
     ]
diff --git a/wagtail/wagtailimages/migrations/0001_initial.py b/wagtail/wagtailimages/migrations/0001_initial.py
index c8ad0a2948..b87a212d5e 100644
--- a/wagtail/wagtailimages/migrations/0001_initial.py
+++ b/wagtail/wagtailimages/migrations/0001_initial.py
@@ -5,8 +5,8 @@ import taggit.managers
 from django.conf import settings
 from django.db import migrations, models
 
-import wagtail.wagtailadmin.taggable
 import wagtail.wagtailimages.models
+import wagtail.wagtailsearch.index
 
 
 class Migration(migrations.Migration):
@@ -54,7 +54,7 @@ class Migration(migrations.Migration):
             options={
                 'abstract': False,
             },
-            bases=(models.Model, wagtail.wagtailadmin.taggable.TagSearchable),
+            bases=(models.Model, wagtail.wagtailsearch.index.Indexed),
         ),
         migrations.CreateModel(
             name='Rendition',