I was saved from myself this morning. About 30 seconds before the market opened I entered a limit order to buy 200 shares of MKSI at the offer 13.40 (I thought). Shortly after I was filled, I realized that I had just paid 15.399! I entered the order by clicking on the offer (TWS) so either the offer changed or I didn't notice the two dollar difference. I called IB and got a rep in less than a minute. I explained what had happened, and he said he would call Island and get back with me. About an hour later, he called me back and told me that the trade was being broken. I was glad to not lose the $400. I have three reasons for posting this. First, a reminder to watch the dollars - especially before/after the close. Second, I wanted to give IB credit for doing a good job. Third, I really didn't know if the trade would be broken because it was before the open. Was someone kind enough to let me off the hook? Or, are clearly erroneous trades broken even before the market is open?