textbook problem SO2 vs SO3

[Monica Soliman 3F]

in the textbook, it asks to place these three in decreasing bond length, they were SO2, SO3, and SO32-. we know that SO32- is the longest because it has a single bond, however, when you compare SO3 and SO2 one has three double bonds (SO3) and the other is two double bonds(SO2) In the answer key however they say that so2 and so2 are equal? How is that possible?

[Faith St Amant 3D]

I think they're equal because each bond is the same length, even though there are is one more double bond in SO3 than there is in SO2. So, when they say to compare bond lengths, since they both have the same types of bonds in there and no other types are present, they have equal bond length.