diff --git a/lisp/custom.el b/lisp/custom.el
index 70b6839db3..49330bb1a4 100644
--- a/lisp/custom.el
+++ b/lisp/custom.el
@@ -146,6 +146,10 @@ custom-declare-variable
 set to nil, as the value is no longer rogue."
   (put symbol 'standard-value (purecopy (list default)))
   ;; Maybe this option was rogue in an earlier version.  It no longer is.
+  (let ((ht #s(hash-table size 65 test eql rehash-size 1.5 rehash-threshold 0.8 data
+                          (foo bar))))
+    (unless (eq 'bar (gethash 'foo ht))
+      (error (format "This shouldn't be happening. Hash table: %s" ht))))
   (when (get symbol 'force-value)
     (put symbol 'force-value nil))
   (if (keywordp doc)