diff --git a/guides/source/i18n.md b/guides/source/i18n.md
index e623f8cf8a15b306bbc72d5cdd44660355940789..1565008a699d2a5685a18c0693c4396d69ae962f 100644
--- a/guides/source/i18n.md
+++ b/guides/source/i18n.md
@@ -888,6 +888,7 @@ So, for example, instead of the default error message `"cannot be blank"` you co
 | inclusion    | -                         | :inclusion                | -             |
 | exclusion    | -                         | :exclusion                | -             |
 | associated   | -                         | :invalid                  | -             |
+| non-optional association | -             | :required                 | -             |
 | numericality | -                         | :not_a_number             | -             |
 | numericality | :greater_than             | :greater_than             | count         |
 | numericality | :greater_than_or_equal_to | :greater_than_or_equal_to | count         |