diff --git a/xorriso/xorriso.1 b/xorriso/xorriso.1
index f3b232f1..794b1e1c 100644
--- a/xorriso/xorriso.1
+++ b/xorriso/xorriso.1
@@ -1875,6 +1875,12 @@ It might also be that your operating system has a session limit with mount.
 Always have a blank media ready to perform a full backup in case the update
 attempt fails. An overview of sessions is given by option -toc.
 .br
+Sessions on multi-session media are separated by several MB of unused blocks.
+So with small sessions the payload capacity can become substantially lower
+than the overall media capacity. If the remaining space on media does not
+suffice for the next gap, the drive is supposed to close the media
+automatically.
+.br
 \fBBetter do not use your youngest backup for -update_r\fR.
 Have at least two media which you use alternatingly. So only older backups
 get endangered by the new write operation, while the newest backup is