diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 0875fca369a..cb19644cbe1 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -12,6 +12,8 @@
 
 	* simple.el (font-info): Declare.
 
+	* subr.el (x-popup-dialog): Declare.
+
 	* window.el (x-display-pixel-height, tool-bar-lines-needed): Declare.
 	(fit-frame-to-buffer): Explicit error if --without-x.
 	(mouse-autoselect-window-select): Silence compiler.
diff --git a/lisp/subr.el b/lisp/subr.el
index adf3f9a97f2..b903ef1ea96 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -2239,6 +2239,9 @@ floating point support."
 	    (push read unread-command-events)
 	    nil))))))
 
+;; Behind display-popup-menus-p test.
+(declare-function x-popup-dialog "xmenu.c" (position contents &optional header))
+
 (defun y-or-n-p (prompt)
   "Ask user a \"y or n\" question.  Return t if answer is \"y\".
 PROMPT is the string to display to ask the question.  It should