Using constexpr in a namespace with static_assert is giving error

I have declared the following in header file.

namespace G1
{
    inline namespace V1
    {
        constexpr float getV();
    }
}

In CPP file, I have defined the getV function as

constexpr float G1::V1::getV()
{
    return 0.1f;
}

In the main I am using static_assert to compare the version as shown.

int main()
{
    static_assert( G1::getV() == 1.0f, "Error"); // Please Ignore the way I am comparing the floats
    return 0;
}

But when I compile the code, I am getting expression did not evaluate to a constant.

Am I doing anything wrong here? I am using VS2015. Thanks in advance