[1.7.x] Note re migrations importing custom fields

Backport of b4d486c80f from master

1 files changed, 3 insertions, 1 deletions

diff --git a/docs/topics/migrations.txt b/docs/topics/migrations.txt
index 461801fb34..685c716f3c 100755
--- a/docs/topics/migrations.txt
+++ b/docs/topics/migrations.txt
@@ -333,7 +333,9 @@ They will, however, have the same fields, relationships and ``Meta`` options
 
 References to functions in field options such as ``upload_to`` and
 ``limit_choices_to`` are serialized in migrations, so the functions will need
-to be kept around for as long as there is a migration referencing them.
+to be kept around for as long as there is a migration referencing them. Any
+:doc:`custom model fields </howto/custom-model-fields>` will also need to be
+kept, since these are imported directly by migrations.
 
 In addition, the base classes of the model are just stored as pointers,
 so you must always keep base classes around for as long as there is a migration