diff --git a/guides/source/active_record_basics.md b/guides/source/active_record_basics.md
index a67e2924d7..b0d4bbd2c0 100644
--- a/guides/source/active_record_basics.md
+++ b/guides/source/active_record_basics.md
@@ -105,9 +105,9 @@ depending on the purpose of these columns.
   fields that Active Record will look for when you create associations between
   your models.
 * **Primary keys** - By default, Active Record will use an integer column named
-  `id` as the table's primary key. When using [Active Record
-  Migrations](active_record_migrations.html) to create your tables, this column will be
-  automatically created.
+  `id` as the table's primary key (`bigint` for Postgres and MYSQL, `integer`
+  for SQLite). When using [Active Record Migrations](active_record_migrations.html)
+  to create your tables, this column will be automatically created.
 
 There are also some optional column names that will add additional features
 to Active Record instances: