INDIANAPOLIS (AP) — An Indiana Republican leader says he was stunned to learn U.S. Rep. Todd Young might have failed to meet a state ballot requirement in his U.S. Senate campaign.

Senate President Pro Tem David Long said Thursday he’s waiting for official word from state election officials that Young failed to gather the 500 required petition signatures from each of Indiana’s nine congressional districts. But Long says, if true, it would be “one of the most colossal mistakes” he’s seen.

State Democratic officials filed a complaint Wednesday, challenging Young’s placement on the May primary ballot.

An Associated Press review of Young’s petitions from northwestern Indiana’s 1st Congressional District found he was three signatures short.

Long has endorsed U.S. Rep. Marlin Stutzman, the other Republican running to replace retiring GOP Sen. Dan Coats.