TemplateSpecializationTypeLoc cannot be derived from Using Template

I am trying to obtain the location of template specialization for a type that is declared with using statement like this: template <class T> using vec = std::vector<T>.

I’m trying the following:

// var is a clang::VarDecl
auto info = var->getTypeSourceInfo();
auto Specialization = info->getTypeLoc().castAs<clang::TemplateSpecializationTypeLoc>();

It works for a type defined like template <class T> class my_type { ... };, but not for using in which it emitts a casting error.

What type should I use instead of TemplateSpecializationTypeLoc to obtain the source info of a declaration with a type defined by using keyword?