diff --git a/man/man1/notmuch-search.1 b/man/man1/notmuch-search.1
index d3391f83..59e8f341 100644
--- a/man/man1/notmuch-search.1
+++ b/man/man1/notmuch-search.1
@@ -132,8 +132,19 @@ Limit the number of displayed results to N.
 .TP 4
 .BR \-\-exclude=(true|false|flag)
 
-Specify whether to omit messages matching search.tag_exclude from the
-search results (the default) or not. The extra option
+A message is called "excluded" if it matches at least one tag in
+search.tag_exclude that does not appear explicitly in the search terms.
+This option specifies whether to omit excluded messages in the search
+process.
+
+The default value,
+.BR true ,
+prevents excluded messages from matching the search terms.
+
+.B false
+allows excluded messages to match search terms and appear in displayed
+results. Excluded messages are still marked in the relevant outputs.
+
 .B flag
 only has an effect when
 .B --output=summary