Help?? The output says "Walkspeed is not a valid member of Humanoid"

So, for however long you hold the left mouse button, the players walkspeed increases however long you hold it. It just errors out. Please help!!

Player = game.Players.LocalPlayer
Character = Player.Character
Torso = Character.Torso
Mouse = Player:GetMouse()
hold = false

Mouse.Button1Down:connect(function()

    if hold == false then
        hold = true
        while hold == true do
            Player.Character.Humanoid.Walkspeed = Player.Character.Humanoid.Walkspeed +1
    local   Brick = Instance.new("Part", Player)
            Brick.Position = Player.Position
            Brick.BrickColor = BrickColor.new("New Yeller")
            Brick.Transparency = 0.7

        end
    end

end)



Mouse.Button1Up:connect(function()
    if hold == true then
        hold = false
    end
end)