c++11 call to member function is ambiguous

class Base{
public:
    void func(double a) = delete;
    void func(int a) const {}
};

int main(){
    Base base;

    base.func(1);
    return 0;
}

This code compiled using clang++ produces following error:

clang++ --std=c++11 test.cpp 
test.cpp:22:7: error: call to member function 'func' is ambiguous
    base.func(1);

With g++ warning is produced:

g++ -std=c++11 test.cpp 
test.cpp: In function ‘int main()’:
test.cpp:22:13: warning: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second: base.func(1);

Why this code is ambiguous ?