diff --git a/lisp/nxml/rng-uri.el b/lisp/nxml/rng-uri.el
index 77fed8c32d..242238e0d1 100644
--- a/lisp/nxml/rng-uri.el
+++ b/lisp/nxml/rng-uri.el
@@ -68,7 +68,7 @@ Signal an error if URI is not a valid file URL."
 
 ;; pattern is either nil or match or replace
 (defun rng-uri-file-name-1 (uri pattern)
-  (unless (string-match "\\`\\(?:[^%]\\|%[[:xdigit:]]{2}\\)*\\'" uri)
+  (unless (string-match "\\`\\(?:[^%]\\|%[[:xdigit:]]\\{2\\}\\)*\\'" uri)
     (rng-uri-error "Bad escapes in URI `%s'" uri))
   (setq uri (rng-uri-unescape-multibyte uri))
   (let* ((components
@@ -312,7 +312,7 @@ Both FULL and BASE must be absolute URIs."
 (defun rng-uri-unescape-unibyte (str)
   (replace-regexp-in-string "%[0-7][[:xdigit:]]"
 			    (lambda (h)
-			      (string-to-number (substring h 1) 16))
+			      (string (string-to-number (substring h 1) 16)))
 			    str
 			    t
 			    t))
@@ -325,8 +325,8 @@ Both FULL and BASE must be absolute URIs."
 				(regexp-quote
 				 (if (= (length match) 1)
 				     match
-				   (string-to-number (substring match 1)
-						     16)))))
+				   (string (string-to-number (substring match 1)
+						     16))))))
 			    str
 			    t
 			    t))