Assuming the coils of the pickup are wired correctly, the way the pickup is wired to the circuitry means it should work as a single coil.
Does it hum more than when you use the other pickup on the guitar (or if it's a single pickup guitar, more than other humbucker equipped guitars)? If so, there you go.
A quick measurement with a digital multimeter would clarify the situation.
Cheers Stephan