If A Salesperson Made A Pricing Mistake, Would You Honor The Deal?

The Situation
David has been selling for ABC Enterprises for several years. He was asked by a prospect to provide a pricing quote. In his haste to provide pricing quickly, he made a mistake and priced the account too low. The mistake was not discovered until after the prospect agreed to the deal.
Based on the pricing provided by David, the company is losing 20% on this account. David realizes he made a mistake and is unsure how to resolve this issue without losing the client. Sheepishly, he comes into your office and asks what to do.
Your Challenge
Do you honor the pricing? If so, how do you reconcile losing money on a client?
If not, how do you address this with the client?