How Do You Prevent a Cylinder Part From Rotating? Help!

I placed this script in the cylinder part:

function onTouched()
    script.Parent.CFrame = CFrame.new(script.Parent.Position.X, script.Parent.Position.Y - 0.2, script.Parent.Position.Z)
end

script.Parent.Touched:connect(onTouched)

When I touch the cylinder part, it's rotation goes from (0, 0, -90) to (0, 0, 0)! How can I prevent this? Thank you!