In TClassEdit and TDictionary there are enums which define Multimap=5 and Set=6. In TStreamerElement these are reversed. The result of this is that when saving a set<> object to a tree the stltype is incorrectly set. This results in MakeProject generating a #inclde multimap line instead of #include set. ( Incidentally, for a multimap stl object the correct include would anyway be #include map). I have fixed it by making all the enums consistent. I did this by reversing the definitions of set and multimap in TStreamerElement.h, but I don't know if that might have other consequences. This appears to be new in patch 10 of v 5.34 where the code in TStreamerInfo::Build() has been modified to use a new constructor in TStreamerSTL which uses a TVirtualCollectionProxy.