Wells Fargo Securities has a new message for investors: Hold on tight.

Christopher Harvey, the firm's head of equity strategy, believes the Turkey debt crisis will spark a crisis of confidence in the United States as earnings season winds down, and headline risks become front and center again.

"You can start to have a lot more wild swings in the marketplace," he said Tuesday on CNBC's "Futures Now." "What we're telling clients is 'don't light your hair on fire. Start to take down risk prudently, and selectively."

But make no mistake, Harvey isn't turning bearish. It's the potential for stomach-churning waves of volatility, that could throw investors, he said. It's not the actual dip.

"We don't think we'll see much of a sell-off. If we do see a sell-off, we think it's in or around 2 to 3 percent," said Harvey, who's maintaining his year-end price target of 2,950. It would be a gain of about 4 percent from current levels.

"We are still constructive on the market, but we think people need to be a lot more selective today than they have been in the past," he said.

To ride out the volatility, Harvey is telling clients to reduce exposure to technology and other momentum areas of the market. He contends they could get hurt the most.

"It's going to be painful, but it will be healthy. The market will be more discriminating as we move forward," Harvey said. "Start cycling into more defensive equities: your staples, your utilities, your REITs, more of your bond proxies at the margin."