diff --git a/README.asciidoc b/README.asciidoc
index 39aef0f1..00f618ad 100644
--- a/README.asciidoc
+++ b/README.asciidoc
@@ -792,6 +792,8 @@ Some of Kakoune state is available through environment variables:
  * `kak_buf_line_count`: the current buffer line count
  * `kak_timestamp`: timestamp of the current buffer, the timestamp is an
        integer value which is incremented each time the buffer is modified.
+ * `kak_curr_history_id`: history id of the current buffer, the history id is an integer value
+       which is used to reference a specific buffer version in the undo tree
  * `kak_runtime`: directory containing the kak binary
  * `kak_count`: count parameter passed to the command
  * `kak_opt_<name>`: value of option <name>
diff --git a/doc/manpages/expansions.asciidoc b/doc/manpages/expansions.asciidoc
index 5e4bdc79..3f01bb84 100644
--- a/doc/manpages/expansions.asciidoc
+++ b/doc/manpages/expansions.asciidoc
@@ -74,6 +74,9 @@ informations about Kakoune's state:
 *kak_timestamp*::
 	timestamp of the current buffer, the timestamp is an integer value
 	which is incremented each time the buffer is modified
+*kak_curr_history_id*::
+	history id of the current buffer, the history id is an integer value
+	which is used to reference a specific buffer version in the undo tree
 *kak_runtime*::
 	directory containing the kak binary
 *kak_count*::