diff --git a/src/ikarus.boot b/src/ikarus.boot
index e4cecfd..99859a2 100644
Binary files a/src/ikarus.boot and b/src/ikarus.boot differ
diff --git a/src/ikarus.bytevectors.ss b/src/ikarus.bytevectors.ss
index fd2a184..048d08f 100644
--- a/src/ikarus.bytevectors.ss
+++ b/src/ikarus.bytevectors.ss
@@ -5,6 +5,7 @@
           bytevector-copy! u8-list->bytevector bytevector->u8-list
           bytevector-fill! bytevector-copy bytevector=?
           bytevector-uint-ref bytevector-sint-ref 
+          bytevector-uint-set!
           bytevector->uint-list bytevector->sint-list)
   (import 
     (except (ikarus) 
@@ -13,6 +14,7 @@
         bytevector-copy! u8-list->bytevector bytevector->u8-list
         bytevector-fill! bytevector-copy bytevector=?
         bytevector-uint-ref bytevector-sint-ref
+        bytevector-uint-set!
         bytevector->uint-list bytevector->sint-list)
     (ikarus system $fx)
     (ikarus system $pairs)
@@ -340,8 +342,40 @@
                       '() sref-little 'bytevector->sint-list)]
           [(big)    (bytevector->some-list x size ($bytevector-length x) 
                       '() sref-big 'bytevector->sint-list)]
-          [else (error who "invalid endianness ~s" endianness)])))
-    )
+          [else (error who "invalid endianness ~s" endianness)]))))
+
+  (module (bytevector-uint-set!)
+    (define (little-uint-set! x k n size)
+      (cond
+        [($fx= size 0) 
+         (unless (zero? n) 
+           (error 'bytevector-uint-set! "value out of range"))]
+        [else
+         (let-values ([(q r) (quotient+remainder n 256)])
+           (little-uint-set! x ($fxadd1 k) q ($fxsub1 size))
+           ($bytevector-set! x k r))]))
+    (define (big-uint-set! x k1 n k2)
+      (cond
+        [($fx= k1 k2) 
+         (unless (zero? n)
+           (error 'bytevector-uint-set! "value out of range"))]
+        [else
+         (let-values ([(q r) (quotient+remainder n 256)])
+           (let ([k2 ($fxsub1 k2)])
+             (big-uint-set! x k1 q k2)
+             ($bytevector-set! x k2 r)))]))
+    (define bytevector-uint-set!
+      (lambda (x k n endianness size)
+        (define who 'bytevector-uint-set!)
+        (unless (bytevector? x) (error who "~s is not a bytevector" x))
+        (unless (and (fixnum? k) ($fx>= k 0)) (error who "invalid index ~s" k))
+        (unless (and (fixnum? size) ($fx>= size 1)) (error who "invalid size ~s" size))
+        (unless (or (fixnum? n) (bignum? n)) (error who "invalid value ~s" n))
+        (case endianness
+          [(little) (little-uint-set! x k n size)]
+          [(big)    (big-uint-set! x k n ($fx+ k size))]
+          [else (error who "invalid endianness ~s" endianness)]))))
+
 
 
 
diff --git a/src/makefile.ss b/src/makefile.ss
index c2d44c4..57a586d 100755
--- a/src/makefile.ss
+++ b/src/makefile.ss
@@ -285,6 +285,7 @@
     [bytevector=?            i]
     [bytevector-uint-ref     i]
     [bytevector-sint-ref     i]
+    [bytevector-uint-set!    i]
     [bytevector->uint-list   i]
     [bytevector->sint-list   i]
 
diff --git a/src/tests/bytevectors.ss b/src/tests/bytevectors.ss
index 5f14b1e..23c3318 100644
--- a/src/tests/bytevectors.ss
+++ b/src/tests/bytevectors.ss
@@ -85,6 +85,26 @@
     [(lambda (x) (equal? x '(513 -253 513 513)))
      (let ([b (u8-list->bytevector '(1 2 3 255 1 2 1 2))])
        (bytevector->sint-list b 'little 2))]
+    [(lambda (x) (equal? x '(#xfffffffffffffffffffffffffffffffd
+                             -3
+                             (253 255 255 255 255 255 255 255
+                              255 255 255 255 255 255 255 255))))
+     (let ([b (make-bytevector 16 -127)])
+       (bytevector-uint-set! b 0 (- (expt 2 128) 3) 'little 16)
+       (list 
+         (bytevector-uint-ref b 0 'little 16)
+         (bytevector-sint-ref b 0 'little 16)
+         (bytevector->u8-list b)))]
+    [(lambda (x) (equal? x '(#xfffffffffffffffffffffffffffffffd
+                             -3
+                             (255 255 255 255 255 255 255 255
+                              255 255 255 255 255 255 255 253))))
+     (let ([b (make-bytevector 16 -127)])
+       (bytevector-uint-set! b 0 (- (expt 2 128) 3) 'big 16)
+       (list 
+         (bytevector-uint-ref b 0 'big 16)
+         (bytevector-sint-ref b 0 'big 16)
+         (bytevector->u8-list b)))]
     ))