diff --git a/README.asciidoc b/README.asciidoc
index 39aef0f1..2c96216a 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_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..72f6daa3 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_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*::
diff --git a/src/main.cc b/src/main.cc
index 66394627..19a6d400 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -93,6 +93,10 @@ void register_env_vars()
             "timestamp", false,
             [](StringView name, const Context& context) -> String
             { return to_string(context.buffer().timestamp()); }
+        }, {
+            "history_id", false,
+            [](StringView name, const Context& context) -> String
+            { return to_string(context.buffer().current_history_id()); }
         }, {
             "selection", false,
             [](StringView name, const Context& context)