diff --git a/lib/libsys/aio_cancel.2 b/lib/libsys/aio_cancel.2
--- a/lib/libsys/aio_cancel.2
+++ b/lib/libsys/aio_cancel.2
@@ -80,6 +80,13 @@
 .Fa fildes
 argument
 is an invalid file descriptor.
+.It Bq Er ENOSYS
+The
+.Fn aio_cancel
+system call is not supported.
+This can occur if
+.Xr aio 4
+support is not present.
 .El
 .Sh SEE ALSO
 .Xr aio_error 2 ,
diff --git a/lib/libsys/aio_error.2 b/lib/libsys/aio_error.2
--- a/lib/libsys/aio_error.2
+++ b/lib/libsys/aio_error.2
@@ -72,6 +72,13 @@
 .Fa iocb
 argument
 does not reference an outstanding asynchronous I/O request.
+.It Bq Er ENOSYS
+The
+.Fn aio_error
+system call is not supported.
+This can occur if
+.Xr aio 4
+support is not present.
 .El
 .Sh SEE ALSO
 .Xr aio_cancel 2 ,
diff --git a/lib/libsys/aio_fsync.2 b/lib/libsys/aio_fsync.2
--- a/lib/libsys/aio_fsync.2
+++ b/lib/libsys/aio_fsync.2
@@ -136,6 +136,13 @@
 is not a valid descriptor.
 .It Bq Er EINVAL
 This implementation does not support synchronized I/O for this file.
+.It Bq Er ENOSYS
+The
+.Fn aio_fsync
+system call is not supported.
+This can occur if
+.Xr aio 4
+support is not present.
 .El
 .Pp
 If the request is successfully enqueued, but subsequently cancelled
diff --git a/lib/libsys/aio_mlock.2 b/lib/libsys/aio_mlock.2
--- a/lib/libsys/aio_mlock.2
+++ b/lib/libsys/aio_mlock.2
@@ -98,6 +98,13 @@
 The asynchronous notification method in
 .Fa iocb->aio_sigevent.sigev_notify
 is invalid or not supported.
+.It Bq Er ENOSYS
+The
+.Fn aio_mlock
+system call is not supported.
+This can occur if
+.Xr aio 4
+support is not present.
 .El
 .Pp
 If the request is successfully enqueued, but subsequently cancelled
diff --git a/lib/libsys/aio_read.2 b/lib/libsys/aio_read.2
--- a/lib/libsys/aio_read.2
+++ b/lib/libsys/aio_read.2
@@ -173,6 +173,13 @@
 The asynchronous notification method in
 .Fa iocb->aio_sigevent.sigev_notify
 is invalid or not supported.
+.It Bq Er ENOSYS
+The
+.Fn aio_read
+system call is not supported.
+This can occur if
+.Xr aio 4
+support is not present.
 .It Bq Er EOPNOTSUPP
 Asynchronous read operations on the file descriptor
 .Fa iocb->aio_fildes
@@ -263,7 +270,9 @@
 .Fn aio_read2
 and
 .Fn aio_readv
-system calls are FreeBSD extensions,
+system calls are
+.Fx
+extensions,
 and should not be used in portable code.
 .Sh HISTORY
 The
diff --git a/lib/libsys/aio_return.2 b/lib/libsys/aio_return.2
--- a/lib/libsys/aio_return.2
+++ b/lib/libsys/aio_return.2
@@ -79,6 +79,13 @@
 and the value of the
 .Fa aio_lio_opcode
 is invalid.
+.It Bq Er ENOSYS
+The
+.Fn aio_return
+system call is not supported.
+This can occur if
+.Xr aio 4
+support is not present.
 .El
 .Sh SEE ALSO
 .Xr aio_cancel 2 ,
diff --git a/lib/libsys/aio_suspend.2 b/lib/libsys/aio_suspend.2
--- a/lib/libsys/aio_suspend.2
+++ b/lib/libsys/aio_suspend.2
@@ -89,6 +89,13 @@
 variable, or at least one of the requests is not valid.
 .It Bq Er EINTR
 the suspend was interrupted by a signal.
+.It Bq Er ENOSYS
+The
+.Fn aio_suspend
+system call is not supported.
+This can occur if
+.Xr aio 4
+support is not present.
 .El
 .Sh SEE ALSO
 .Xr aio_cancel 2 ,
diff --git a/lib/libsys/aio_waitcomplete.2 b/lib/libsys/aio_waitcomplete.2
--- a/lib/libsys/aio_waitcomplete.2
+++ b/lib/libsys/aio_waitcomplete.2
@@ -91,8 +91,6 @@
 .Fn aio_waitcomplete
 system call fails if:
 .Bl -tag -width Er
-.It Bq Er EINVAL
-The specified time limit is invalid.
 .It Bq Er EAGAIN
 The process has not yet called
 .Fn aio_read
@@ -101,6 +99,15 @@
 .It Bq Er EINTR
 A signal was delivered before the timeout expired and before any
 asynchronous I/O requests completed.
+.It Bq Er EINVAL
+The specified time limit is invalid.
+.It Bq Er ENOSYS
+The
+.Fn aio_waitcomplete
+system call is not supported.
+This can occur if
+.Xr aio 4
+support is not present.
 .It Bq Er EWOULDBLOCK
 .It Bq Er EINPROGRESS
 The specified time limit expired before any asynchronous I/O requests
diff --git a/lib/libsys/aio_write.2 b/lib/libsys/aio_write.2
--- a/lib/libsys/aio_write.2
+++ b/lib/libsys/aio_write.2
@@ -182,6 +182,13 @@
 The asynchronous notification method in
 .Fa iocb->aio_sigevent.sigev_notify
 is invalid or not supported.
+.It Bq Er ENOSYS
+The
+.Fn aio_write
+system call is not supported.
+This can occur if
+.Xr aio 4
+support is not present.
 .It Bq Er EOPNOTSUPP
 Asynchronous write operations on the file descriptor
 .Fa iocb->aio_fildes
@@ -265,7 +272,9 @@
 .Fn aio_write2
 and
 .Fn aio_writev
-system calls are FreeBSD extensions,
+system calls are
+.Fx
+extensions,
 and should not be used in portable code.
 .Sh HISTORY
 The