Using a std::vector

I have a function that creates a vector, then calls a class constructor with that vector as an input, but it returns with an error saying

undefined reference to Class::Class(std::vector<double, std::allocator<double> >)

The class has a constructor for a

std::vector<double>

but not a

std::vector<double, std::allocator<double> >

Some example code:

std::vector<double> x1;
std::vector<double> x2;
std::vector<double> myvec;
double thisX;

for (int i=0; i<x1.size(); i++ {
    thisX = x1[i];
    myvec.push_back(thisX);
}
for (int i=0; i<x2.size(); i++ {
    thisX = x2[i];
    myvec.push_back(thisX);
}

Class MyClass( myvec );
// has a constructor for std::vector<double>
// compiler throws the undefined reference to 
// Class::Class(std::vector<double, std::allocator<double> >)

Any insight is appreciated! I'm relatively new to C++ if it wasn't obvious.