diff --git a/lisp/custom.el b/lisp/custom.el
index 5ece5047a86..96dfb37d862 100644
--- a/lisp/custom.el
+++ b/lisp/custom.el
@@ -1692,6 +1692,7 @@ Each of the arguments ARGS has this form:
     (VARIABLE IGNORED)
 
 This means reset VARIABLE.  (The argument IGNORED is ignored)."
+  (declare (obsolete nil "29.1"))
     (apply #'custom-theme-reset-variables 'user args))
 
 (defun custom-add-choice (variable choice)