There’s likely a multitude of reasons behind General Motors’ decision to sell Opel/Vauxhall to PSA Group. However, Automotive News is learning that at least some of the calculus behind the decision may stem from the next version of the Opel Corsa, which was becoming a major pain-point for GM.

The Opel Corsa is the brand’s B-segment car, one of the highest-volume segments in the European market. Opel launched a new Corsa back in 2015, but the car is based on the same Fiat-derived platform that underpinned its predecessor.

Supplier sources tell Automotive News that GM was at a crossroads with the next-generation Corsa. The Fiat platform is too old to continue using, but to switch the car to a GM platform would literally price the car out of the emerging markets. If the sources are to be believed, GM was running out of options when it came to Corsa. And Corsa is critical to Opel meeting European Union CO2 regulations.

“One of the primary reasons [behind the sale] was GM had to develop a whole new B-segment platform just for the Corsa in order for Opel to meet future CO2 emission regulations,” an account manager at an Opel supplier told the publication.

Over the past four years the EU Commission has warned Opel that they are lagging behind the rest of Europe’s automakers in terms of CO2 emissions. As of 2015 the brand was ranked dead last in terms of emissions, behind even luxury brands such as BMW and Mercedes-Benz.

Poor fuel economy and use of heavy, sturdy GM platforms have led to Opel lagging behind in CO2 emissions. It’s a problem the next Corsa will have to combat head-on.

GM President Dan Ammann hinted at this issue while speaking to reporters at the Geneva Motor Show by saying that “The requirements for Europe are becoming more and more unique.” The requirements being CO2 regulations.

So while many factors played into GM’s Opel transaction, it sounds like the inflection point may have ultimately been one little car.