diff --git a/man2/ioprio_set.2 b/man2/ioprio_set.2
index c1dd64c00..7745d8e31 100644
--- a/man2/ioprio_set.2
+++ b/man2/ioprio_set.2
@@ -56,15 +56,23 @@ is interpreted, and has one of the following values:
 .B IOPRIO_WHO_PROCESS
 .I who
 is a process ID or thread ID identifying a single process or thread.
+If
+.I who
+is 0, then operate on the calling thread.
 .TP
 .B IOPRIO_WHO_PGRP
 .I who
 is a process group ID identifying all the members of a process group.
+If
+.I who
+is 0, then operate on the process group of which the caller is a member.
 .TP
 .B IOPRIO_WHO_USER
 .I who
 is a user ID identifying all of the processes that
 have a matching real UID.
+.\" FIXME who==0 needs to be documented, 
+.\" See http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=652443
 .PP
 If
 .I which