Fiserv now ranks above Visa Inc. V-0.95% and Fidelity National Information Services Inc. FIS+1.81% , the next largest short plays in the data-processing and outsourced-services sector with upwards of $4.5 billion in short interest each. Fidelity National Information Services is involved in a mega-merger of its own, after announcing in March that it would be buying Worldpay Inc. WP+1.72% in a cash-and-stock deal valued at $43 billion.

Short interest in Fiserv has mounted in recent months, even as the stock has climbed. Bears are staring down $791 million in mark-to-market losses so far in 2019, and as the shorting continues, S3’s Ihor Dusaniwsky thinks that “the buildup in short interest is more than a merger-[arbitrage] position.” Bears might also be making a bet that Fiserv will disappoint with its next quarterly report, due out Thursday after the closing bell.

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Just yesterday, Fiserv bears shorted another 1 million shares, bringing total shares shorted to 55.78 million. So far this year, the company has seen shares shorted climb by 760%, or 49.3 million shares, but Dusaniwsky says the activity might ease up in the coming days.