diff --git a/doc/pages/expansions.asciidoc b/doc/pages/expansions.asciidoc
index fe3e4a13..f97cb472 100644
--- a/doc/pages/expansions.asciidoc
+++ b/doc/pages/expansions.asciidoc
@@ -86,6 +86,8 @@ informations about Kakoune's state:
     directory containing the user configuration
 *kak_count*::
     count parameter passed to the command
+*kak_register*::
+    register parameter passed to the command
 *kak_opt_<name>*::
     value of option *name*
 *kak_reg_<r>*::