SQLite does not update

im trying to update the value of the column "done" for an entry. COLUMN_DONE saves an Integer.

public void markAsDone(int date_id, int t_id){
        SQLiteDatabase db = getWritableDatabase();
        String query = "UPDATE " + TABLE_DATES_T + " SET " + COLUMN_DONE + "= 1 WHERE date_id IS '" + date_id + "' AND t_id IS '" + t_id + "'";
        db.execSQL(query);
        db.close();
    }

But it doesnt update the value of this entry. What did I wrong???