diff --git a/postgres/day-of-week-for-a-date.md b/postgres/day-of-week-for-a-date.md
index 0540076..5bb8688 100644
--- a/postgres/day-of-week-for-a-date.md
+++ b/postgres/day-of-week-for-a-date.md
@@ -19,4 +19,7 @@ function
          6
 ```
 
+The days of week are `0` through `6`, `0` being Sunday and `6` being
+Saturday.
+
 [source](http://www.postgresql.org/docs/current/static/functions-datetime.html)