diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2
index 9120bdf40..014c0b5c1 100644
--- a/man2/ioctl_userfaultfd.2
+++ b/man2/ioctl_userfaultfd.2
@@ -208,6 +208,11 @@ signal will be sent to the faulting process.
 Applications using this
 feature will not require the use of a userfaultfd monitor for processing
 memory accesses to the regions registered with userfaultfd.
+.TP
+.BR UFFD_FEATURE_THREAD_ID " (since Linux 4.14)"
+If this feature bit is set,
+.I uffd_msg.pagefault.feat.ptid
+will be set to the faulted thread ID for each page fault message.
 .PP
 The returned
 .I ioctls