diff --git a/pitfall/restructure/bitfield-test.rkt b/pitfall/restructure/bitfield-test.rkt
new file mode 100644
index 00000000..f1091570
--- /dev/null
+++ b/pitfall/restructure/bitfield-test.rkt
@@ -0,0 +1,53 @@
+#lang restructure/racket
+(require "bitfield.rkt" "number.rkt" "stream.rkt" "buffer.rkt" rackunit racket/match)
+
+#|
+approximates
+https://github.com/mbutterick/restructure/blob/master/test/Bitfield.coffee
+|#
+
+;describe 'Bitfield', ->
+;  bitfield = new Bitfield uint8, ['Jack', 'Kack', 'Lack', 'Mack', 'Nack', 'Oack', 'Pack', 'Quack']
+;  JACK  = 1 << 0
+;  KACK  = 1 << 1
+;  LACK  = 1 << 2
+;  MACK  = 1 << 3
+;  NACK  = 1 << 4
+;  OACK  = 1 << 5
+;  PACK  = 1 << 6
+;  QUACK = 1 << 7
+
+(define bitfield (+Bitfield uint8 '(Jack Kack Lack Mack Nack Oack Pack Quack)))
+(match-define (list JACK KACK LACK MACK NACK OACK PACK QUACK)
+  (map (curry arithmetic-shift 1) (range 8)))
+
+;
+;  it 'should have the right size', ->
+;    bitfield.size().should.equal 1
+
+(check-equal? (send bitfield size) 1)
+
+;
+;  it 'should decode', ->
+;    stream = new DecodeStream new Buffer [JACK | MACK | PACK | NACK | QUACK]
+;    bitfield.decode(stream).should.deep.equal
+;      Jack: yes, Kack: no, Lack: no, Mack: yes, Nack: yes, Oack: no, Pack: yes, Quack: yes
+
+(let ([stream (+DecodeStream (+Buffer (list (bitwise-ior JACK MACK PACK NACK QUACK))))])
+  (for/and ([(k v) (in-hash (send bitfield decode stream))])
+    (check-equal? v (hash-ref #hash((Quack . #t) (Nack . #t) (Lack . #f) (Oack . #f) (Pack . #t) (Mack . #t) (Jack . #t) (Kack . #f)) k))))
+
+
+;
+;  it 'should encode', (done) ->
+;    stream = new EncodeStream
+;    stream.pipe concat (buf) ->
+;      buf.should.deep.equal new Buffer [JACK | MACK | PACK | NACK | QUACK]
+;      done()
+;
+;    bitfield.encode stream, Jack: yes, Kack: no, Lack: no, Mack: yes, Nack: yes, Oack: no, Pack: yes, Quack: yes
+
+(let ([stream (+EncodeStream)])
+  (define h #hash((Quack . #t) (Nack . #t) (Lack . #f) (Oack . #f) (Pack . #t) (Mack . #t) (Jack . #t) (Kack . #f)))
+  (send bitfield encode stream h)
+  (check-equal? (send stream dump) (+Buffer (list (bitwise-ior JACK MACK PACK NACK QUACK)))))
diff --git a/pitfall/restructure/bitfield.rkt b/pitfall/restructure/bitfield.rkt
index b7ed5bba..325692cf 100644
--- a/pitfall/restructure/bitfield.rkt
+++ b/pitfall/restructure/bitfield.rkt
@@ -19,7 +19,7 @@ https://github.com/mbutterick/restructure/blob/master/src/Bitfield.coffee
 
   (define/override (size . args) (send type size))
 
-  (define/augment (encode stream flag-hash)
+  (define/augment (encode stream flag-hash [ctx #f])
     (define bitfield-int (for/sum ([(flag i) (in-indexed flags)]
                                    #:when (and flag (hash-ref flag-hash flag)))
                            (expt 2 i)))