diff --git a/README.asciidoc b/README.asciidoc
index 044ffdc9..2c6ebe5f 100644
--- a/README.asciidoc
+++ b/README.asciidoc
@@ -975,6 +975,7 @@ contain some special data:
  * `%`: current buffer name
  * `.`: current selection contents
  * `#`: selection indices (first selection has 1, second has 2, ...)
+ * `_`: null register, always empty
 
 Default registers
 ^^^^^^^^^^^^^^^^^
diff --git a/doc/manpages/registers.asciidoc b/doc/manpages/registers.asciidoc
index d3ef8085..4ad233df 100644
--- a/doc/manpages/registers.asciidoc
+++ b/doc/manpages/registers.asciidoc
@@ -56,6 +56,9 @@ contain some special data
 *#*::
 	selection indices (first selection has 1, second has 2, ...)
 
+*_*::
+	null register, always empty
+
 Integer registers
 -----------------
 Registers *1* to *9* hold the grouped sub-matches of the regular
diff --git a/src/input_handler.cc b/src/input_handler.cc
index d3081ac9..e674790f 100644
--- a/src/input_handler.cc
+++ b/src/input_handler.cc
@@ -145,6 +145,7 @@ constexpr StringView register_doc =
     "    * .: selection contents\n"
     "    * #: selection index\n"
     "    * [0-9]: selections capture group\n"
+    "    * _: null register\n"
     "    * \": default yank/paste register\n"
     "    * @: default macro register\n"
     "    * /: default search register\n"