diff --git a/lisp/mail/emacsbug.el b/lisp/mail/emacsbug.el
index e55f950aac3..795516737d3 100644
--- a/lisp/mail/emacsbug.el
+++ b/lisp/mail/emacsbug.el
@@ -69,6 +69,7 @@
 (declare-function x-server-vendor "xfns.c" (&optional terminal))
 (declare-function x-server-version "xfns.c" (&optional terminal))
 (declare-function message-sort-headers "message" ())
+(declare-function w32--os-description "w32-fns" ())
 (defvar message-strip-special-text-properties)
 
 (defun report-emacs-bug-can-use-osx-open ()