Template specialization fails because of unknown template definition

My template specialization does not work. Does anyone know how I can implement this function properly with templates?

template<class T>
float hz_to_nsec(const T &freq) {
    return freq != 0 ? static_cast<float>(NSEC_PER_SEC) / freq : 0;
}

template <>
double hz_to_nsec<double>(const double &freq) {
    return freq != 0 ? static_cast<double>(NSEC_PER_SEC) / freq : 0;
}