The two largest U.S. toy makers could soon unite. 

Hasbro Inc. (HAS) , the maker of Monopoly, has made a takeover offer for its rival Mattel Inc. (MAT) , the maker of Barbie dolls, the Wall Street Journal is reporting.

Shares of Hasbro were rising over 3%, while shares of Mattel surged over 24% in after-hours trading on Friday following the report.

Rumors began swirling about a possible tie-up of the two companies back in February after Mattel posted disastrous 2016 fourth-quarter results. But, at the time, the potential for Hasbro to take over Mattel was met with skepticism.

A Hasbro spokeswoman said that "as a matter of company policy, we do not comment on rumors or speculation."

The Journal said "the terms of a potential deal couldn't be learned, and as always, there may not be one."

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