diff --git a/Doc/using/cmdline.rst b/Doc/using/cmdline.rst
index c73f1e0..9274d8e 100644
--- a/Doc/using/cmdline.rst
+++ b/Doc/using/cmdline.rst
@@ -247,7 +247,8 @@
 
    Force the binary layer of the stdin, stdout and stderr streams (which is
    available as their ``buffer`` attribute) to be unbuffered.  The text I/O
-   layer will still be line-buffered.
+   layer will still be line-buffered if writing to the console, or
+   block-buffered if redirected to a non-interactive file.
 
    See also :envvar:`PYTHONUNBUFFERED`.