Can't change a humanoid's JumpPower?

Having a problem with ROBLOX's new property of the humanoid, "JumpPower". Basically, it changes how high you jump. I don't get an error, but here is my script. It just find all the players and changes their jump height.

for i, plr in pairs(game.Players:GetPlayers()) do
    if plr.Character:WaitForChild("Humanoid") then
        plr.Character.Humanoid.JumpPower = 125
    end
end