CPP is mistaking function parameter types

bool TypeChecker::functions_equal(
        ...
        std::vector<Type*> p_args);

The argument I pass for p_args has the same type:

std::vector<Type*> args;

but for some reason, CPP gives me this error:

no function found with arguments:
TypeChecker::functions_equal(..., std::vector<snowball::Type*>&);

here is my question: why does CPP "deduce" that args has type std::vector<snowball::Type*>&?