diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 81758af..e5740a5 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -5864,7 +5864,7 @@
 		respectively.  3 is reserved for use by the |matchparen|
 		plugin.
 		If the {id} argument is not specified or -1, |matchadd()|
-		automatically chooses a free ID.
+		automatically chooses a free ID, which is at least 1000.
 
 		The optional {dict} argument allows for further custom
 		values. Currently this is used to specify a match specific