diff --git a/lisp/subr.el b/lisp/subr.el
index e630087b68f..8dcaef08b65 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -3432,12 +3432,18 @@ read-number
   (let ((n nil)
 	(default1 (if (consp default) (car default) default)))
     (when default1
-      (setq prompt
-	    (if (string-match "\\(\\):[ \t]*\\'" prompt)
-		(replace-match (format minibuffer-default-prompt-format default1) t t prompt 1)
-	      (replace-regexp-in-string "[ \t]*\\'"
-					(format minibuffer-default-prompt-format default1)
-					prompt t t))))
+      ;; If PROMPT uses `format-prompt', don't duplicate DEFAULT in
+      ;; the prompt string.
+      (if (string-match (regexp-quote
+			 (format minibuffer-default-prompt-format default1))
+			prompt)
+	  (setq default1 nil)
+        (setq prompt
+	      (if (string-match "\\(\\):[ \t]*\\'" prompt)
+		  (replace-match (format minibuffer-default-prompt-format default1) t t prompt 1)
+	        (replace-regexp-in-string "[ \t]*\\'"
+					  (format minibuffer-default-prompt-format default1)
+					  prompt t t)))))
     (while
 	(progn
 	  (let ((str (read-from-minibuffer