London (CNN Business) SoftBank warned Monday that it expected to post its first operating loss in 15 years because of a collapse in the value of its flagship tech investments.

The Japanese company said it expected an operating loss of 1.35 trillion yen ($12.5 billion) in its fiscal year through March 31, 2020. That compares with an operating profit of more than 2 trillion yen the previous year.

blamed the historic losses — the worst in at least 20 years, according to the data provider Refinitiv — on the plunging valuations of investments held by its mega tech fund.

The Vision Fund is expected to report losses amounting to 1.8 trillion yen ($16.7 billion) due to "the deteriorating market environment," the company said in a statement. The markets have been roiled by uncertainty over the coronavirus pandemic

Big losses on other SoftBank investments held outside the $100 billion Vision Fund, notably bankrupt internet satellite startup OneWeb , and troubled coworking provider WeWork , are also expected to weigh heavily on earnings, it added.

SoftBank did not disclose which Vision Fund investments would be written down, but its warning stands out because "nobody forecasts writedowns," according to Dan Baker, an analyst with research firm Morningstar.

Uber UBER Sweeping restrictions on work, travel and social distancing aimed at tackling the coronavirus pandemic have piled pressure on the fund's global tech portfolio, which includes sizable stakes in, Didi, OYO and Grab.

The Vision Fund loss is "much worse than expected; consensus was still expecting an operating profit for the year," CLSA analyst Oliver Matthew wrote in an investor note on Monday.

SoftBank founder and CEO Masayoshi Son, who has cast himself as a bold, visionary investor, has been forced to play defense after some of his biggest bets collapsed in value. Last month he made a surprise announcement of what amounts to a fire sale of $41 billion worth of assets to buy back SoftBank shares and reduce the company's heavy debt load.

With the massive Vision Fund, Son and his company were able to take large stakes in flashy technology startups working on ride-hailing, robotics, agriculture and other areas that he felt were central to shaping the future. By cutting large checks, often totaling the hundreds of millions or even billions of dollars, the fund could help startups expand rapidly and sometimes boosted their valuations significantly.

But even before the recent market turbulence around the coronavirus pandemic, there were sirens flashing around some of SoftBank's bets.

Two of SoftBank's biggest investments — Uber and WeWork — both faced rough receptions on Wall Street in large part due to concerns about their steep losses. Uber was pummeled by investors after going public and continues to trade well below its IPO price. WeWork tried and failed to pull off a public offering and required a bailout from SoftBank . (SoftBank recently walked away from a chunk of the WeWork rescue package.)

"Much of the damage to the (Vision Fund) credibility has already occurred with the very public failed WeWork float," Baker, of Morningstar, said.

All in all, more than 7,300 people lost their jobs across a dozen SoftBank-backed startups in the four months ending in February, according to a CNN Business tally