diff --git a/libguile/strings.c b/libguile/strings.c
index 90dc83a66..ee43e815e 100644
--- a/libguile/strings.c
+++ b/libguile/strings.c
@@ -1,4 +1,5 @@
-/* Copyright (C) 1995,1996,1998,2000,2001, 2004, 2006, 2008, 2009, 2010, 2011, 2012, 2013, 2014 Free Software Foundation, Inc.
+/* Copyright (C) 1995, 1996, 1998, 2000, 2001, 2004, 2006,
+ *   2008-2015 Free Software Foundation, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -1673,9 +1674,9 @@ scm_from_utf8_stringn (const char *str, size_t len)
 
           ascii = 0;
 
-          nbytes = u8_mbtouc (&c, ustr + i, len - i);
+          nbytes = u8_mbtoucr (&c, ustr + i, len - i);
 
-          if (c == 0xfffd)
+          if (nbytes < 0)
             /* Bad UTF-8.  */
             decoding_error (__func__, errno, str, len);
 
diff --git a/libguile/symbols.c b/libguile/symbols.c
index f93833b9d..71d982730 100644
--- a/libguile/symbols.c
+++ b/libguile/symbols.c
@@ -1,5 +1,5 @@
-/* Copyright (C) 1995, 1996, 1997, 1998, 2000, 2001, 2003, 2004,
- *   2006, 2009, 2011, 2013 Free Software Foundation, Inc.
+/* Copyright (C) 1995-1998, 2000, 2001, 2003, 2004, 2006, 2009, 2011,
+ *   2013, 2015 Free Software Foundation, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -164,10 +164,10 @@ utf8_string_equals_wide_string (const scm_t_uint8 *narrow, size_t nlen,
       ucs4_t c;
       int nbytes;
 
-      nbytes = u8_mbtouc (&c, narrow + byte_idx, nlen - byte_idx);
+      nbytes = u8_mbtoucr (&c, narrow + byte_idx, nlen - byte_idx);
       if (nbytes == 0)
         break;
-      else if (c == 0xfffd)
+      else if (nbytes < 0)
         /* Bad UTF-8.  */
         return 0;
       else if (c != wide[char_idx])
diff --git a/test-suite/tests/bytevectors.test b/test-suite/tests/bytevectors.test
index 4cc5b67e0..f8f020a30 100644
--- a/test-suite/tests/bytevectors.test
+++ b/test-suite/tests/bytevectors.test
@@ -1,6 +1,6 @@
 ;;;; bytevectors.test --- R6RS bytevectors. -*- mode: scheme; coding: utf-8; -*-
 ;;;;
-;;;; Copyright (C) 2009-2014 Free Software Foundation, Inc.
+;;;; Copyright (C) 2009-2015 Free Software Foundation, Inc.
 ;;;;
 ;;;; Ludovic Courtès
 ;;;;
@@ -24,6 +24,9 @@
   :use-module (rnrs bytevectors)
   :use-module (srfi srfi-4))
 
+(define exception:decoding-error
+  (cons 'decoding-error "input (locale conversion|decoding) error"))
+
 ;;; Some of the tests in here are examples taken from the R6RS Standard
 ;;; Libraries document.
 
@@ -501,6 +504,15 @@
            (= (string-length str)
               (- (bytevector-length utf8) 2)))))
 
+  (pass-if-equal "utf8->string [replacement character]"
+      '(104 105 65533)
+    (map char->integer
+         (string->list (utf8->string #vu8(104 105 239 191 189)))))
+
+  (pass-if-exception "utf8->string [invalid encoding]"
+      exception:decoding-error
+    (utf8->string #vu8(104 105 239 191 50)))
+
   (pass-if "utf16->string"
     (let* ((utf16  (uint-list->bytevector (map char->integer
                                                (string->list "hello, world"))