diff --git a/src/ikarus.boot b/src/ikarus.boot
index 003bb30..d6f2059 100644
Binary files a/src/ikarus.boot and b/src/ikarus.boot differ
diff --git a/src/ikarus.date-string.ss b/src/ikarus.date-string.ss
index d7602eb..ef20d06 100644
--- a/src/ikarus.date-string.ss
+++ b/src/ikarus.date-string.ss
@@ -1,10 +1,12 @@
 
 (library (ikarus date-string)
   (export date-string)
-  (import (except (ikarus) date-string))
+  (import
+    (rnrs bytevectors)
+    (except (ikarus) date-string))
   (define date-string
     (lambda ()
       (let ([s (make-bytevector 10)])
         (foreign-call "ikrt_bvftime" s 
-          (string->utf8-bytevector "%F"))
-        (utf8-bytevector->string s)))))
+          (string->utf8 "%F"))
+        (utf8->string s)))))
diff --git a/src/ikarus.intel-assembler.ss b/src/ikarus.intel-assembler.ss
index 5ae43d8..e1b31ea 100644
--- a/src/ikarus.intel-assembler.ss
+++ b/src/ikarus.intel-assembler.ss
@@ -4,6 +4,7 @@
   (export assemble-sources code-entry-adjustment)
   (import 
     (ikarus)
+    (rnrs bytevectors)
     (except (ikarus code-objects) procedure-annotation)
     (ikarus system $pairs))
 
@@ -903,7 +904,7 @@
       (let f ([ls mem])
         (cond
           [(null? ls) 
-           (let ([bv (string->utf8-bytevector x)])
+           (let ([bv (string->utf8 x)])
              (set! mem (cons (cons x bv) mem))
              bv)]
           [(string=? x (caar ls)) (cdar ls)]
diff --git a/src/ikarus.io.input-files.ss b/src/ikarus.io.input-files.ss
index ed44a38..2ec2d90 100644
--- a/src/ikarus.io.input-files.ss
+++ b/src/ikarus.io.input-files.ss
@@ -9,6 +9,7 @@
     (ikarus system $strings)
     (ikarus system $bytevectors)
     (ikarus system $chars)
+    (rnrs bytevectors)
     (except (ikarus)
             open-input-file current-input-port console-input-port
             with-input-from-file call-with-input-file
@@ -165,7 +166,7 @@
     (lambda (filename)
       (close-ports)
       (let ([fd/error (foreign-call "ikrt_open_input_file" 
-                        (string->utf8-bytevector filename))])
+                        (string->utf8 filename))])
         (if (fixnum? fd/error)
             (let ([port (make-input-port 
                           (make-input-file-handler fd/error filename)
diff --git a/src/ikarus.io.output-files.ss b/src/ikarus.io.output-files.ss
index 40d02e3..abf3b65 100644
--- a/src/ikarus.io.output-files.ss
+++ b/src/ikarus.io.output-files.ss
@@ -10,6 +10,7 @@
     (ikarus system $chars)
     (ikarus system $bytevectors)
     (ikarus system $fx)
+    (rnrs bytevectors)
     (except (ikarus)
             standard-output-port standard-error-port   
             console-output-port current-output-port    
@@ -132,7 +133,7 @@
       (close-ports)
       (let ([fd/error 
              (foreign-call "ikrt_open_output_file" 
-                           (string->utf8-bytevector filename)
+                           (string->utf8 filename)
                            (option-id options))])
         (if (fixnum? fd/error)
             (let ([port
diff --git a/src/ikarus.io.output-strings.ss b/src/ikarus.io.output-strings.ss
index 5452ab7..57c381c 100644
--- a/src/ikarus.io.output-strings.ss
+++ b/src/ikarus.io.output-strings.ss
@@ -138,7 +138,7 @@
              (set! open? #f)]
             [(port-name p) 'string-port]
             [(get-output-string p) 
-             (utf8-bytevector->string
+             (utf8->string
                (concat 
                  ($port-buffer p) 
                  ($port-index p)
diff --git a/src/ikarus.numerics.ss b/src/ikarus.numerics.ss
index 22db193..bef83ee 100644
--- a/src/ikarus.numerics.ss
+++ b/src/ikarus.numerics.ss
@@ -1177,7 +1177,7 @@
 
   (define bignum->string
     (lambda (x)
-      (utf8-bytevector->string
+      (utf8->string
         (foreign-call "ikrt_bignum_to_bytevector" x))))
   
   (define ratnum->string
@@ -2278,6 +2278,7 @@
 (library (ikarus flonum-conversion)
   (export string->flonum flonum->string)
   (import 
+    (rnrs bytevectors)
     (ikarus system $bytevectors)
     (ikarus system $flonums)
     (except (ikarus) flonum->string string->flonum ))
@@ -2422,7 +2423,7 @@
     (cond
       [(string? x)
        (foreign-call "ikrt_bytevector_to_flonum" 
-         (string->utf8-bytevector x))]
+         (string->utf8 x))]
       [else 
        (error 'string->flonum "~s is not a string" x)])) )
 
diff --git a/src/ikarus.posix.ss b/src/ikarus.posix.ss
index 58724c2..7445e32 100644
--- a/src/ikarus.posix.ss
+++ b/src/ikarus.posix.ss
@@ -3,6 +3,7 @@
   (export posix-fork fork waitpid system file-exists? delete-file
           env environ)
   (import 
+    (rnrs bytevectors)
     (except (ikarus)
        posix-fork fork waitpid system file-exists? delete-file
        env environ))
@@ -31,7 +32,7 @@
       (unless (string? x)
         (error 'system "~s is not a string" x))
       (let ([rv (foreign-call "ik_system"
-                  (string->utf8-bytevector x))])
+                  (string->utf8 x))])
         (if (fx= rv -1)
             (error 'system "failed")
             rv))))
@@ -41,7 +42,7 @@
       (unless (string? x)
         (error 'file-exists? "filename ~s is not a string" x))
       (let ([v (foreign-call "ikrt_file_exists" 
-                  (string->utf8-bytevector x))])
+                  (string->utf8 x))])
         (cond
           [(boolean? v) v]
           [else
@@ -61,7 +62,7 @@
       (unless (string? x)
         (error 'delete-file "filename ~s is not a string" x))
       (let ([v (foreign-call "ikrt_delete_file"
-                 (string->utf8-bytevector x))])
+                 (string->utf8 x))])
         (case v
           [(0) (void)]
           [else
diff --git a/src/ikarus.strings.ss b/src/ikarus.strings.ss
index 9c3e547..c345c82 100644
--- a/src/ikarus.strings.ss
+++ b/src/ikarus.strings.ss
@@ -439,7 +439,7 @@
   (define uuid
     (lambda ()
       (let ([s ($make-bytevector 16)])
-        (utf8-bytevector->string
+        (utf8->string
           (or (foreign-call "ik_uuid" s)
               (error 'uuid "failed!"))))))
   )
diff --git a/src/ikarus.transcoders.ss b/src/ikarus.transcoders.ss
index f3dd903..76e6ceb 100644
--- a/src/ikarus.transcoders.ss
+++ b/src/ikarus.transcoders.ss
@@ -1,8 +1,7 @@
 
 (library (ikarus transcoders)
-  (export string->utf8-bytevector
-          utf8-bytevector->string)
-  (import (except (ikarus) string->utf8-bytevector utf8-bytevector->string)
+  (export string->utf8 utf8->string)
+  (import (except (ikarus) string->utf8 utf8->string)
           (ikarus system $strings)
           (ikarus system $bytevectors)
           (ikarus system $fx)
@@ -22,7 +21,7 @@
   ;;; replace: places a U+FFFD in place of the malformed bytes
   ;;; raise: raises an error
 
-  (define string->utf8-bytevector
+  (define string->utf8
     (lambda (str)
       (define (utf8-string-size str)
         (let f ([str str] [i 0] [j ($string-length str)] [n 0])
@@ -74,14 +73,16 @@
                      ($fxlogor #b10000000 ($fxlogand b #b111111)))
                    (f bv str ($fxadd1 i) ($fx+ j 4) n)])))])))
       (unless (string? str) 
-        (error 'string->utf8-bytevector "~s is not a string" str))
+        (error 'string->utf8 "~s is not a string" str))
       (fill-utf8-bytevector
         ($make-bytevector (utf8-string-size str))
         str)))
 
-  (define utf8-bytevector->string
+  (define (utf8->string x) (decode-utf8-bytevector x 'replace))
+
+  (define decode-utf8-bytevector
     (let ()
-      (define who 'utf8-bytevector->string)
+      (define who 'decode-utf8-bytevector)
       (define (count bv mode)
         (let f ([x bv] [i 0] [j ($bytevector-length bv)] [n 0] [mode mode])
           (cond
@@ -241,7 +242,7 @@
         [(bv) (convert bv 'raise)]
         [(bv handling-mode)
          (unless (memq handling-mode '(ignore replace raise)) 
-           (error 'utf8-bytevector->string
+           (error 'decode-utf8-bytevector
                   "~s is not a valid handling mode"
                   handling-mode))
          (convert bv handling-mode)])))
diff --git a/src/makefile.ss b/src/makefile.ss
index e9ef770..bcd3940 100755
--- a/src/makefile.ss
+++ b/src/makefile.ss
@@ -214,9 +214,6 @@
     [weak-pair?                                  i]
     [uuid                                        i]
     [date-string                                 i]
-    [string->utf8-bytevector                     i]
-    [utf8-bytevector->string                     i]
-    [$two-bignums                                i]
     [andmap                                      i]
     [ormap                                       i]
     [fx<                                         i]
@@ -843,10 +840,10 @@
     [sint-list->bytevector                       i r bv]
     [string->utf16                               r bv]
     [string->utf32                               r bv]
-    [string->utf8                                r bv]
+    [string->utf8                                i r bv]
     [u8-list->bytevector                         i r bv]
     [uint-list->bytevector                       i r bv]
-    [utf8->string                                r bv]
+    [utf8->string                                i r bv]
     [utf16->string                               r bv]
     [utf32->string                               r bv]
     [condition?                                  r co]
diff --git a/src/todo-r6rs.ss b/src/todo-r6rs.ss
index f7986e1..8b4aaa6 100755
--- a/src/todo-r6rs.ss
+++ b/src/todo-r6rs.ss
@@ -407,10 +407,10 @@
     [sint-list->bytevector                      C bv]
     [string->utf16                              S bv]
     [string->utf32                              S bv]
-    [string->utf8                               S bv]
+    [string->utf8                               C bv]
     [u8-list->bytevector                        C bv]
     [uint-list->bytevector                      C bv]
-    [utf8->string                               S bv]
+    [utf8->string                               C bv]
     [utf16->string                              S bv]
     [utf32->string                              S bv]
     ;;;