diff --git a/supabase/migrations/20260125000000_add_sort_date_column.sql b/supabase/migrations/20260125000000_add_sort_date_column.sql
index c79aff4e..cb8133d4 100644
--- a/supabase/migrations/20260125000000_add_sort_date_column.sql
+++ b/supabase/migrations/20260125000000_add_sort_date_column.sql
@@ -2,12 +2,24 @@
 -- This column stores the older of publishedAt (from JSON data) or indexed_at
 -- Used for sorting feeds chronologically by when content was actually published
 
--- Note: We use ::timestamp AT TIME ZONE 'UTC' to make the expression immutable
--- (direct ::timestamptz cast is not immutable as it depends on session timezone)
+-- Create an immutable function to parse ISO 8601 timestamps from text
+-- This is needed because direct ::timestamp cast is not immutable (accepts 'now', 'today', etc.)
+-- The regex validates the format before casting to ensure immutability
+CREATE OR REPLACE FUNCTION parse_iso_timestamp(text) RETURNS timestamptz
+LANGUAGE sql IMMUTABLE STRICT AS $$
+  SELECT CASE
+    -- Match ISO 8601 format: YYYY-MM-DDTHH:MM:SS with optional fractional seconds and Z/timezone
+    WHEN $1 ~ '^\d{4}-\d{2}-\d{2}[T ]\d{2}:\d{2}:\d{2}(\.\d+)?(Z|[+-]\d{2}:?\d{2})?$' THEN
+      $1::timestamptz
+    ELSE
+      NULL
+  END
+$$;
+
 ALTER TABLE documents
 ADD COLUMN sort_date timestamptz GENERATED ALWAYS AS (
   LEAST(
-    COALESCE((data->>'publishedAt')::timestamp AT TIME ZONE 'UTC', indexed_at),
+    COALESCE(parse_iso_timestamp(data->>'publishedAt'), indexed_at),
     indexed_at
   )
 ) STORED;