The Sensex at the Bombay Stock Exchange closed with a marginal loss of 9 points, at 18,385, amid weak Asian markets on Thursday. The Nifty at the National Stock Exchange dropped 6 points or 0.1 percent to 5,521. Stock markets in China, Hong Kong, South Korea and Singapore lost between 0.2 percent and 1.7 percent, as investors remained uncertain about the global economic recovery.