Ambiguous call resolved as CORE::sqrt(), qualify as such or use & at -e line 1.

Thanks. I had tried pre-declaring the sub but I must have stuffed up that test because I certainly didn't see that warning.
I've just double-checked, and the warning is present for me, too.

Update: Oh ... and for the warning to appear, the ambiguity has to be detected at compile time.

Cheers,
Rob.