diff --git a/lib/libc/sys/msync.2 b/lib/libc/sys/msync.2
index e755aa1810e7..d69d7ad9ede9 100644
--- a/lib/libc/sys/msync.2
+++ b/lib/libc/sys/msync.2
@@ -30,7 +30,7 @@
 .\" SUCH DAMAGE.
 .\"
 .\"	from: @(#)msync.2	8.1 (Berkeley) 6/9/93
-.\"	$Id: msync.2,v 1.5 1994/06/21 04:24:53 cgd Exp $
+.\"	$Id: msync.2,v 1.6 1994/06/21 04:49:04 cgd Exp $
 .\"
 .Dd June 9, 1993
 .Dt MSYNC 2
@@ -63,6 +63,23 @@ will also take place at this time.
 Filesystem operations on a file that is mapped for shared modifications
 are unpredictable except after an
 .Fn msync .
+.Sh ERRORS
+The following errors may be reported:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+The
+.Fa addr
+parameter was not page aligned.
+.It Bq Er EINVAL
+The
+.Fa addr
+parameter did not specify an address part of a mapped region.
+.It Bq Er EINVAL
+The
+.Fa len
+parameter was negative.
+.It Bq Er EIO
+An I/O error occured while writing to the file system.
 .Sh SEE ALSO
 .Xr madvise 2 ,
 .Xr munmap 2 ,