After a long, impressive run, Boeing Co (NYSE:BA) stock has returned to Earth in March. BA stock hit an all-time high of $183, only to pull back about 4% over the past two weeks. A downgrade of the stock by Morgan Stanley last week further took the wind out of Boeing’s sails.

Obviously, that’s not quite a collapse, and BA shares are still up 49% from 52-week lows.

But investors would be wise to consider taking profits. I’ve been a bit skeptical of the Boeing share price gains for some time now — and I think investors might do well to heed Morgan Stanley’s advice and exit BA stock at current altitude.

Too Many Investors Love Boeing Stock

Wall Street analysts can sometimes be a contrarian indicator, but Morgan Stanley analyst Rajeev Lalwani at least is trying to follow those contrarian indicators. Lalwani upgraded BA stock in June, in part because “sentiment is poor on Boeing and it may be time for a change.”

A 35% gain since that note shows that Lalwani’s initial thesis played out well. Boeing stock last year was plagued with longer-term concerns about demand cycles, competition in China and low oil prices. (Lower oil prices lead to lower jet fuel prices. Lower jet fuel prices give less incentive for carriers like Delta Air Lines, Inc. (NYSE:DAL) and Southwest Airlines Co (NYSE:LUV) to upgrade to more fuel-efficient airplanes.)

Sentiment now has changed markedly — even if a lot of those concerns haven’t. As the old saying goes, when everyone loves a stock, there’s no one left to buy. Boeing stock may not quite be at those levels, but the pool of buyers certainly is smaller than it was last spring.

BA Stock Multiples Have a Bit Too Much Air

Meanwhile, Lalwani pointed out that BA’s valuation is a bit stretched at current levels. Boeing stock trades near 18 times 2018 earnings-per-share, against a 16.5x multiple for peers (likely including Airbus, Lockheed Martin Corporation (NYSE:LMT), and Raytheon Company (NYSE:RTN)) and a 17x multiple for the market as a whole.

That type of valuation seems to limit potential appreciation in BA stock, simply because multiple expansion is limited. While Boeing is a great company, aerospace isn’t a great business. It’s highly cyclical, sales and profits are uneven and sales and product cycles take years. And at this point, only ~23% of BA revenue comes from (usually) more stable defense spending.

Boeing stock only rarely gets a multiple above the market as a whole, but that’s where it’s trading now. And that would seem to imply that the earnings multiple could come down a bit, with each turn taking 5%+ off BA shares.

How to Play Boeing

Again, Boeing stock looks expensive at $180, but not ridiculously so. Paying 18x forward EPS for an industry leader isn’t necessarily a foolish decision. Boeing could be a potential beneficiary of a border adjustment tax, or corporate tax reform more broadly. There may still be some room for cost-cutting, as Deutsche Bank analyst Myles Walton argued just last week.

And a dividend yielding 3.2% means BA stock should provide some return even if its stock price flatlines.

To enter the stock, however, I’d prefer a much better price, and a margin of safety. Existing Boeing stock investors could consider selling out-of-the-money calls. The January 2018 $195 call trades for $6.70 or so at the moment. Investors could more than double their income from BA stock, while giving away any upside over 9% from current levels.

Personally, I think that type of upside is unlikely in the near-term. Boeing stock has performed well, to be sure. But I think Morgan Stanley makes some good points in its argument to exercise some caution at current levels. After all, nothing can fly forever.

As of this writing, Vince Martin did not hold a position in any of the aforementioned securities.