Northrop Grumman (NYSE:NOC) on Friday was downgraded to Market Perform from an investment rating of Outperform by analysts at Cowen. They said the aerospace and defense company’s warning about losing money on developing the B-21 Raider stealth bomber is reason for caution.

When Northrop (NOC) reported quarterly results, it said there’s a possibility of a $1.2 billion loss during the first five years of what’s known as low-rate initial production (LRIP) of the nuclear bomber, which the company and the U.S. Air Force publicly unveiled last month.

“At this point we don’t believe that a loss is probable,” David Keffer, CFO of Northrop (NOC), said during the company’s regularly scheduled call with analysts and investors. “We do believe that a loss is possible.”

The disclosure in a regulatory filing of a “reasonably possible” loss on the B-21 work “looks like an extended overhang to what’s been the sector’s cleanest growth story,” according to Cowen. “Northrop Grumman’s (NOC) fundamentals are otherwise healthy, and we see continuing strong support for defense spending.”

Cowen lowered its price target for Northrop (NOC) to $478 a share from $500 a share, based on an enterprise value-to-EBITDA multiple of 15 times 2023 estimated results.

Northrop (NOC) declined 4.2% on Thursday after reporting earnings that beat Wall Street’s estimates.