Twitter’s largest acquisition to date, of the adtech business TellApart, has turned out to be a little less big than originally thought. Back in April 2015, it was calculated that Twitter would pay nearly $533 million for TellApart based on the company’s share price at the time. But a 10-K report published today notes the final numbers: It was nearly $54 million lower, at $479.1 million, with $395 million of that recorded as goodwill.

The reason for the reduced final price? The company’s declining stock value, and the fact that the deal was almost entirely done in shares. Twitter paid $22.6 million in cash for TellApart, plus a further 12.2 million shares of its common stock valued at $456.5 million (not including shares and options for employees who were coming over with the deal).

At the time of the deal in April, Twitter’s stock was valued at $42.27 and the deal was for 12.6 million shares. It seems that by the time the deal closed in May 2015, the share number had declined to 12.2 million, with an additional portion in cash alongside the shares.

That wasn’t the worst drop Twitter has seen, though. As a measure of how much the price has dropped since, today the company is trading at roughly $18/share. Unsurprisingly, Twitter has been in the midst of trying to turn around its business. It picked up a new CEO, co-founder Jack Dorsey, in October 2015, and the company has been trying to figure out new features and ways to attract more Twitter users beyond its existing user base of occasional Tweeters/Lurkers and die-hard heavy users.

The TellApart acquisition preceded the bigger of these changes. It was made when Dick Costolo — who also invested in TellApart (ahem) — was still CEO, and Twitter’s interest in the company speaks more to its ongoing push to generate more revenue, regardless of whatever changes may be underway in the consumer-facing non-ad product.

TellApart’s technology is used in retargeting services, helping Twitter track ads and users across web and mobile platforms both on Twitter and elsewhere, and to ensure that those who buy because of a Twitter ad get noted.

There is an indication that TellApart could be paying for itself in a relatively short time: Twitter pointed out in the 10-K that ad revenue from services on third-party websites was up to $194.2 million in 2015, compared to only $11.4 million in 2014, “driven, in part, by the acquisition of TellApart.”

Twitter further itemized the TellApart acquisition as follows:

“$21.4 million to developed technology, $43.3 million to advertiser relationships, $2.1 million to trade name, $29.6 million to cash acquired, $19.7 million to account receivables acquired, which are expected to be substantially collected, $2.2 million to other tangible assets acquired, $11.8 million to liabilities assumed, $22.4 million to deferred tax liability recorded, and the excess $395.0 million of the purchase price over the fair value of net assets acquired was recorded as goodwill,” which it describes as “the expected synergies from potential monetization opportunities and from integrating the retargeting technologies into the Company’s mobile platforms, and the value of acquired talent.”

In addition to TellApart, there’s some other data on Twitter acquisitions last year. Although eight Twitter acquisitions were made public in 2015, the company singles out four in the 10-K form. Without naming any of them (we have contacted Twitter for more detail), it notes that the four together accounted for a total purchase price of $118.9 million, with common stock worth $60.1 million and $58.8 million in cash.

The breakdown of assets, Twitter says, includes “$12.9 million for developed technologies, $3.2 million to net tangible assets acquired based on their estimated fair value on the acquisition date, $3.4 million to deferred tax liability, and the excess $106.2 million of the purchase price over the fair value of net assets acquired to goodwill.”

In all, 2015 was Twitter’s biggest year in terms of acquisition values. In 2014, the company spent just over $322.2 million in cash and shares on buying companies, including just over $134 million for Gnip, the firehose provider that is behind Twitter’s moves into more big-data and enterprise services.

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