diff --git a/man2/futex.2 b/man2/futex.2
index 566bd7cda..beb487e97 100644
--- a/man2/futex.2
+++ b/man2/futex.2
@@ -682,6 +682,13 @@ to returning to user space.
 Unlike the other futex operations described above,
 the PI futex operations are designed
 for the implementation of very specific IPC mechanisms).
+.\"
+.\" FIXME We don't quite have a definition anywhere of what a PI futex
+.\"       is (vs a non-PI futex). Below, we have the information of
+.\"       FUTEX_CMP_REQUEUE_PI requeues from a non-PI futex to a
+.\"       PI futex, but what determines whether the futex is of one
+.\"       kind of the other? We should have such a definition somewhere
+.\"       about here.
 
 PI futexes are operated on by specifying one of the following values in
 .IR futex_op :