WiX: Old versions don't disappear in Add/Remove Programs list

I have a Windows Service that I install and upgrade with WiX, and this works great (it's very fast!). The only problem is that if I upgrade from, say, 1.0 to 1.1, both copies still have entries in the Add/Remove Programs list.

So how can I make sure WiX removes its old/outdated entries in the Add/Remove Programs list when I perform an update?