Is there a reason to use std::int64_t from

In C++11 we are provided with fixed-width integer types, such as std::int32_t and std::int64_t, which are defined in cstdint/cinttypes. However, int32_t and int64_t are also in stdint.h/inttypes.h. What are the reasons to use std::int64_t over int64_t? To me, the former involves more typing, even by using namespace std.