diff --git a/db/migrate/20260319062845_add_index_to_users_lower_login_on_postgres_and_sqlite.rb b/db/migrate/20260319062845_add_index_to_users_lower_login_on_postgres_and_sqlite.rb
new file mode 100644
index 000000000..7c4fe70d6
--- /dev/null
+++ b/db/migrate/20260319062845_add_index_to_users_lower_login_on_postgres_and_sqlite.rb
@@ -0,0 +1,13 @@
+class AddIndexToUsersLowerLoginOnPostgresAndSqlite < ActiveRecord::Migration[8.1]
+  def up
+    if Redmine::Database.postgresql? || Redmine::Database.sqlite?
+      add_index :users, "(lower(login))", name: "index_users_on_lower_login"
+    end
+  end
+
+  def down
+    if index_exists?(:users, name: "index_users_on_lower_login")
+      remove_index :users, name: "index_users_on_lower_login"
+    end
+  end
+end