diff --git a/docs/ref/models/fields.txt b/docs/ref/models/fields.txt
index fbd9fb78f8e..8d61b90e1d2 100644
--- a/docs/ref/models/fields.txt
+++ b/docs/ref/models/fields.txt
@@ -59,6 +59,9 @@ string, not ``NULL``.
     coerced for string-based fields that have the empty string as a possible
     value, and the value ``NULL`` will be stored to denote the empty string.
 
+If you want to accept :attr:`~Field.null` values with :class:`BooleanField`,
+use :class:`NullBooleanField` instead.
+
 ``blank``
 ---------
 
@@ -341,6 +344,9 @@ A true/false field.
 
 The admin represents this as a checkbox.
 
+If you need to accept :attr:`~Field.null` values then use
+:class:`NullBooleanField` instead.
+
 .. versionchanged:: 1.2
 
     In previous versions of Django when running under MySQL ``BooleanFields``