diff --git a/man/man1/tagger.1 b/man/man1/tagger.1
index 80a42e0..3e01a6e 100644
--- a/man/man1/tagger.1
+++ b/man/man1/tagger.1
@@ -62,6 +62,8 @@ option is implied, and can be omitted.
 .It Fl a, \-add Ar tag
 Add the specified tag.
 This option can be used multiple times.
+Adding a tag that is already present in a file will not add it a second time, so
+tags always remain unique for any given file.
 .It Fl c, \-change Ar tag
 Change the given tag, into a new value supplied as an argument for the
 .Fl i
@@ -75,6 +77,11 @@ These pairs of
 and
 .Fl i
 options can be used multiple times.
+.Pp
+If a tag is changed into a tag that already exists for a file, it is not added a
+second time, so tags will always remain unique for any given file.
+This situation would be equivalent to simply delete the original tag which
+should be changed.
 .It Fl d, \-delete Ar tag
 Delete the given tag, if it exists.
 This option can be used multiple times.