(CNN) Congress will approve a total of $425 million in election security funding, according to two sources familiar with the deal.

The money, which comes in the appropriations bill set to be released Monday, is a compromise: significantly higher than the $250 million Senate Majority Leader Mitch McConnell had initially backed in September, but far below the more than $1 billion that the Democrat-controlled House had passed in HR 1 in March

It's the biggest influx of cash to bolster US election infrastructure since the 2016 election, which prompted a gradual national consensus that voting machines that don't use paper ballots or receipts -- and thus can't be independently verified with an audit -- are outdated. Congress also passed $380 million for election security in the appropriations bill of 2018.

Virginia Democratic Sen. Mark Warner praised the existence of the funding, but echoed election security experts in arguing that states should get a promise of regular annual funding to better plan their security strategy.

"This is a welcome development after months of pressure, but this money is no substitute for a permanent funding mechanism for securing and maintaining elections systems, and comprehensive legislation to protect our elections, which the White House and Republican leaders in Congress have been blocking for two years now," Warner told CNN.

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