File.lockingBinaryWriter is not output range?

[Denis Feklushkin]

/+ dub.sdl:
name "hello_world"
+/

import std.algorithm, std.range, std.stdio;

void main()
{
     // lockingBinaryWriter: Returns an output range that locks 
the file and allows fast writing to it.
     // 
https://dlang.org/library/std/stdio/file.locking_binary_writer.html

     stdout.lockingBinaryWriter.put(cast(byte) 123); // works

     // But this assert is false:
     static 
assert(isOutputRange!(typeof(stdout.lockingBinaryWriter), byte));
}

This blocks to user File as Stream for msgpack-d.