c++ partial template specialization with requires statement: error: out-of-line definition of 'foo' from class Bar<T> without definition

Consider the following code which attempts to implement a partial specialization of class Bar. In the first case, the foo member function is defined inline and in the second case out of line. The out of line definition produces a compile error which I cannot figure out:

error: out-of-line definition of 'foo' from class 'Bar<T>' without definition

template<class T>
struct Bar;

template<class T>
requires std::is_same_v<T, int>
struct Bar<T> {
    int foo(T a) {
        return a + 5;
    }
};

template<class T>
requires std::is_same_v<T, double>
struct Bar<T> {
    double foo(T a);
};

template<class T>
requires std::is_same_v<T, double>
double Bar<T>::foo(T a) {
    return a + 5;
};

I am using clang-11 with the c++20 compilation option. I am unsure if this is my misunderstanding, a feature or a bug. Any help is appreciated.