C++: Default template argument only deduced when using "<>"

I created this struct for some easy templated Math definitions:

template<class T = float> struct Math{
    static constexpr T PI = T(3.14159265359);
    static constexpr T E = T(2.718281828459);
    static constexpr T INF = std::numeric_limits<T>::infinity();
};

I would like to use it like this:

float pi = Math::PI;

Even if the default argument T is float Ill get the error:

'template<class T> struct Math' used without template parameters

If I use Math<>::PI it works. Is this a compiler bug or are the <> brackets mandatory?