diff --git a/backend/src/rmfdb/cli.py b/backend/src/rmfdb/cli.py
index 4940d52..25a2d15 100644
--- a/backend/src/rmfdb/cli.py
+++ b/backend/src/rmfdb/cli.py
@@ -171,7 +171,7 @@ def generate_sitemap(app):
                                 ')', '%29'
                             )
                         ),
-                        'lastmod': item.updated_at.isoformat()
+                        'lastmod': item.updated_at.strftime('%Y-%m-%d')
                     }
                 )
         sitemap = Environment().from_string(template).render(pages=pages)