Conversion looses qualifier

ALL,

Could someone please explain why following:

class Document
{
public:
    std::vector &GetVector() const { return m_myStringVector; };
private:
    std::vector m_myStrngVector;
};

gives:

 error C2440: 'return': cannot convert from 'const std::vector<std::wstring,std::allocator<_Ty>>' to 'std::vector<std::wstring,std::allocator<_Ty>> &'
          with
          [
              _Ty=std::wstring
          ]
note: Conversion loses qualifiers

It is a simple getter and don't need to be declared as const.

What am I missing?