Wrong rapidjson conversion from uint64 to string

I need to output a Uint64 number a = 1185345998335 to file using rapidjson library. I write

writer.Uint64(a);

and debugger says that it's exactly a which is passed into a function. But the output is 4229991935, which is exactly 4 last bytes of the number, and the first 4 bytes are lost.

00000113 fc208dff 1185345998335
00000000 fc208dff 0004229991935