diff --git a/runtime/doc/popup.txt b/runtime/doc/popup.txt
index 6a2471a..d11557c 100644
--- a/runtime/doc/popup.txt
+++ b/runtime/doc/popup.txt
@@ -591,7 +591,7 @@
 
 The first argument of |popup_create()| (and the second argument to
 |popup_settext()|) specifies the text to be displayed, and optionally text
-properties.  It is in one of four forms:
+properties.  It is in one of four forms:  *E1284*
 - a buffer number
 - a string
 - a list of strings