diff --git a/docs/text-sizing-protocol.rst b/docs/text-sizing-protocol.rst
index ae9bfe2bb..e8ceea5ec 100644
--- a/docs/text-sizing-protocol.rst
+++ b/docs/text-sizing-protocol.rst
@@ -1,6 +1,8 @@
 The text sizing protocol
 ==============================================
 
+.. versionadded:: 0.40.0
+
 Classically, because the terminal is a grid of equally sized characters, only
 a single text size was supported in terminals, with one minor exception, some
 characters were allowed to be rendered in two cells, to accommodate East Asian