diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index e1d0bce2ad..036674ef14 100644
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -650,7 +650,7 @@ minibuffer-prompt-properties--setter
                                  "26.1")
 
              (display-fill-column-indicator display-fill-column-indicator
-                                 boolean "27.1")
+                                 boolean "27.1" :safe booleanp)
              (display-fill-column-indicator-column display-fill-column-indicator
                                  (choice
                                   (const :tag "Use fill-column variable"
@@ -659,9 +659,9 @@ minibuffer-prompt-properties--setter
                                          :value 70
                                          :format "%v")
                                   integer)
-                                 "27.1")
+                                 "27.1" :safe (lambda (value) (or (booleanp value) (integerp value))))
              (display-fill-column-indicator-character display-fill-column-indicator
-                                 character "27.1")
+                                 character "27.1" :safe characterp)
 	     ;; xfaces.c
 	     (scalable-fonts-allowed display boolean "22.1")
 	     ;; xfns.c