Nasdaq OMX Group Inc. said it is changing its initial public offering trading procedures following glitches in Facebook Inc.'s market debut that left some traders unsure if their orders for shares had been completed.

The exchange operator said in a statement on Monday that modifications to its IPO procedures would prevent a repetition of the Friday problems with Facebook.

Nasdaq Chief Executive Robert Greifeld said in a conference call with reporters on Sunday that there had been a malfunction in the trading system's design for processing order cancellations.

That led to a more than 40-minute delay in Facebook's debut, following which some traders were unable to find out if their buy and sell orders had been executed.

The Securities and Exchange Commission said it was investigating the issues.

Nasdaq said on Monday it has engaged federal regulators to untangle the problems that occurred, which could eventually result in financial restitution for investors who did not get shares at the desired price.

The Financial Industry Regulatory Authority will review requests from investors whose orders were not filled at the opening price of $42 or were filled at a lower price, Nasdaq said in a statement.

Shares of Facebook tumbled below their issue price of $38 on Monday and ended down 11% at $34.03.

Facebook was the first U.S. company to go public with a valuation greater than $100 billion.