diff --git a/docs/howto/custom-model-fields.txt b/docs/howto/custom-model-fields.txt
index aa14c3cb4e..0cfb70112c 100644
--- a/docs/howto/custom-model-fields.txt
+++ b/docs/howto/custom-model-fields.txt
@@ -491,7 +491,7 @@ accepted lookup types to ``exact`` and ``in``::
         def get_db_prep_lookup(self, lookup_type, value):
             # We only handle 'exact' and 'in'. All others are errors.
             if lookup_type == 'exact':
-                return self.get_db_prep_value(value)
+                return [self.get_db_prep_value(value)]
             elif lookup_type == 'in':
                 return [self.get_db_prep_value(v) for v in value]
             else: