The odds on Democrat candidate Kamala Harris winning next week’s U.S. presidential election are rising on betting platform Polymarket, with some observers suggesting the increase reflects hedging positions among traders who’ve also bet on a victory for her Republican rival, Donald Trump.

Harris’ odds have risen to almost 39% from 33% on Oct. 30. Trump’s odds dropped in tandem, suggestive of lower expectations of him winning, though at 61%, he’s still the preferred candidate. Some market watchers attributed Friday’s crypto market slide to Trump’s slump on Polymarket: The CoinDesk 20 Index (CD20) has dropped 4.4% in the past 24 hours.

Polymarket is fundamentally a betting market place where users can buy “shares” in the outcome of any prediction, winning $1 per share if the outcome occurs. If a Yes share for an event costs $0.60, the market interprets this as a 60% chance of the event occurring.

The odds are dynamic, changing with each trade. Polymarket works on a blockchain-based order book that lists all the buy (bid) and sell (ask) orders for shares in an outcome, similar to how any asset exchange works.

The market’s relatively low liquidity can induce wild swings in prices, with one large purchase briefly driving Trump shares up to 99% last week.

The increase in the price for Harris’ shares could reflect traders buying them as a hedge on their Trump bets, market observers say, as some allege reports of voting irregularities pitted against Trump that could influence market bets.

At current prices, a $10,000 punt on a Harris victory could equal a $25,000 payout if she wins. That’s a 150% return on capital. For large holders of Trump’s win shares, a bet on Harris’ win acts as a hedge.

Polymarket data shows a flurry of activity in trades of more than $10,000 in the past 12 hours with large amounts of Harris “yes” shares and Trump “no” shares being purchased.

Clumpyclumsy, a Polymarket user who joined in October, has alone purchased over $250,000 in Harris “yes” shares since early Friday.

Some users on X also pointed out an arbitrage opportunity for traders participating in various election-based markets.

“Theres a great arbitrage at the moment if you can access both Robinhood Securities and Polymarket,” noted @Kevin_Bolger. “You can load a bag on Trump on Robinhood, another on Harris on Polymarket and whoever wins, you win – assuming transaction fees dont eat the difference. Big difference between both.”

Such market activity comes as Trump and allies allege election fraud in key states, claiming voting irregularities even as local election officials push back.