Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of infrastructure construction company MasTec (NYSE:MTZ) sank 11% today after its current-quarter guidance disappointed Wall Street.

So what: The stock has pulled back sharply in recent months on signs of slowing demand, and today's downbeat Q2 view only reinforces that worrisome trend. In fact, management blamed the weak outlook on weaker than expected oil and gas segment results, as well as delays in wireless project spending activity, prompting investors to get out of MasTec on the risk of more bad news ahead. 

Now what: Management now sees Q2 adjusted EBITDA of $105 million and EPS of $0.40 on revenue of about $1.1 billion. "While we are being negatively affected by real-time, short-term changes in our wireless business, our long-term outlook remains extremely positive," said CEO Jose Mas. "Across all of our business, we are enjoying very active levels of opportunities which we believe will provide substantial growth in the markets we serve. The fundamentals that will drive this growth remain in place." More importantly, with the stock now off about 30% from its 52-week highs and trading at a forward P/E in the low-teens, the downside might be limited enough to buy into that optimism.