University of Pennsylvania’s Wharton School finance professor Jeremy Siegel has made some big calls on the stock market in very public forums for years.

Siegel is credited with predicting the dot-com crash about a year before it happened. He was pounding the table on Dow 20,000 (that has obviously been proven correct with the Dow currently above 31,000) before anyone else was even thinking about it.

So it’s not a total shock Siegel is standing pat with his latest prediction for 2021: Despite yawning fears of on the Street of a market top, fueled by frenzied buying in heavily shorted stocks like struggling GameStop. Siegel still sees the Dow reaching 35,000 this year, at least.

“I am very bullish on the market,” Siegel told Yahoo Finance Live. “We are going to have a boom year. I think stocks definitely have another 20%.”

Siegel acknowledges there could be a bit of near-term choppiness in the market, however. Again, he looks right on that one too.

The Dow Jones Industrial Average plunged more than 2% (550 points) on Friday, mirroring the losses on the S&P 500 and Nasdaq Composite. Over the past five sessions, all three major indices are down about 3%. Meanwhile, Wall Street’s once hot “reflation trade” — consisting of buying banks and other cyclicals on hopes for a strong second half economic rebound — have petered out.

Pros cite several concerns starting to pile up on the market.

First are the ongoing difficulties in rolling out a COVID-19 vaccine across the country. Second, concerns have mounted on the ability of existing COVID-19 vaccines being able to resist new strains of the virus. Given these worries, Wall Street is beginning to question their rosy outlooks for corporate profits later this year (which were driven by vaccine optimism).

“On the vaccine front, the Novavax vaccine was only 60% effective against the South African strain, and while that’s not a material negative, it does add to concern about mutant COVID strains extending the pandemic,” Sevens Report Research founder Tom Essaye said.

And then perhaps the largest concern right now is the insane trading activity in well-shorted stocks such as GameStop and Koss Corporation. Experts believe the rampant buying by day traders reflects behavior typical to a top in the broader stock market.

“I think this [frenzied buying by day traders] is a sign that we are getting to a top and we are going to get a pullback. That’s just one of the signs,” warned Morgan Stanley Investment Management managing director and senior portfolio manager Andrew Slimmon.

Indeed, stocks are experiencing their first air-pocket of 2021 after enjoying bumper gains to cap off a strong 2020. All that means: Dow 35,000 is getting a bit further away.