Chief Justice John Roberts switched his vote behind the scenes to block a citizenship question from appearing on the 2020 census, CNN reported Thursday.

Roberts wrote the opinion and cast the deciding vote in the June decision that effectively blocked the Trump administration from asking the question. Civil rights and other advocacy groups lauded the ruling, noting that adding the question would have caused fewer people, particularly immigrants and minorities, to respond to the decennial survey.

After the case was argued in April, Roberts was poised to side with the Trump administration and allow the question, according to CNN, citing sources familiar with the court’s deliberations. But then Roberts changed his mind, believing that the Trump administration’s reason for adding the question ― better enforcement of the Voting Rights Act ― wasn’t true, CNN reported. In his opinion for the court, Roberts wrote that the rationale “seems to have been contrived.”

It is extremely unusual for private deliberations among Supreme Court justices to become public. The most recent example came in 2012, when CBS reported Roberts switched his vote to preserve the Affordable Care Act.

Emails made public in litigation showed Commerce Secretary Wilbur Ross, who oversees the Census Bureau, sought to add the question long before the Justice Department requested he do so. Emails showed the Commerce Department had asked the Justice Department to request the question on the census.

Many observers had previously speculated that Roberts switched sides in the case. The majority of his opinion explained why the Trump administration could lawfully ask a citizenship question. But ultimately the direction swerved when Roberts wrote that the Trump administration had not adequately provided justification.

After the ruling, President Donald Trump, after some hesitation, ultimately dropped his effort to get the question on the 2020 census. Instead, he instructed Census Bureau officials to gather citizenship data from administrative records. Census officials have since indicated they will make citizenship data available for state officials when they draw new political districts in 2021. The officials could then use the data to draw districts based only on the citizen voting age population, not the total population, which would give Republicans an advantage.

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This article originally appeared on HuffPost.