diff --git a/api.yaml b/api.yaml
index 386e9bb..40c35a2 100644
--- a/api.yaml
+++ b/api.yaml
@@ -309,6 +309,7 @@ components:
         modified:
           type: string
           description: A RFC3339 formatted date when the article was modified
+          nullable: true
         link:
           type: string
           description: Link to the article itself