diff --git a/pitfall/pitfall/document.rkt b/pitfall/pitfall/document.rkt
index 376e5ed8..cd735df0 100644
--- a/pitfall/pitfall/document.rkt
+++ b/pitfall/pitfall/document.rkt
@@ -24,13 +24,11 @@
 
 (define mixed% (annotation-mixin (image-mixin (text-mixin (fonts-mixin (color-mixin (vector-mixin object%)))))))
 
-(define pdf-version 1.3)
-
 (define-subclass mixed% (PDFDocument [options (mhash)])
   (compress-streams? (hash-ref options 'compress #t))
   (current-doc-offset 0)
   
-  (field [byte-strings empty]
+  (field [doc-byte-strings empty]
          [_pageBuffer null]
          [_offsets (mhash)] ; The PDF object store
          [_ended #f]
@@ -73,7 +71,7 @@
        (hash-set! info key val))
 
   ;; Write the header
-  (write this (format "%PDF-~a" pdf-version)) ;  PDF version
+  (write this (format "%PDF-~a" (current-pdf-version))) ;  PDF version
   (write this (string-append "%" (list->string (map integer->char (make-list 4 #xFF))))) ; 4 binary chars, as recommended by the spec
 
   ;; Add the first page
@@ -128,7 +126,7 @@
   (define bstr (if (not (isBuffer? x))
                    (newBuffer (string-append x "\n"))
                    x))
-  (push-field! byte-strings this bstr)
+  (push-field! doc-byte-strings this bstr)
   (current-doc-offset (+ (current-doc-offset) (buffer-length bstr))))
 
 
@@ -212,7 +210,7 @@
   ;; here we'll do it manually
   (define this-output-port (· this output-port))
   (copy-port (open-input-bytes
-              (apply bytes-append (reverse (· this byte-strings)))) this-output-port)
+              (apply bytes-append (reverse (· this doc-byte-strings)))) this-output-port)
   (close-output-port this-output-port))
 
 
diff --git a/pitfall/pitfall/param.rkt b/pitfall/pitfall/param.rkt
index bb5c7992..6a8e8088 100644
--- a/pitfall/pitfall/param.rkt
+++ b/pitfall/pitfall/param.rkt
@@ -2,4 +2,6 @@
 (provide (all-defined-out))
 (define test-mode (make-parameter #f))
 (define compress-streams? (make-parameter #f))
+
+(define current-pdf-version (make-parameter 1.3))
 (define current-doc-offset (make-parameter 'doc-offset-not-initialized))
\ No newline at end of file
diff --git a/pitfall/pitfall/reference.rkt b/pitfall/pitfall/reference.rkt
index a1010019..be6b80d8 100644
--- a/pitfall/pitfall/reference.rkt
+++ b/pitfall/pitfall/reference.rkt
@@ -14,7 +14,7 @@
 (provide PDFReference)
 
 (define-subclass object% (PDFReference document id [payload (mhash)])
-  (field [byte-strings empty]
+  (field [ref-byte-strings empty]
          [offset #f])
 
   (as-methods
@@ -25,14 +25,14 @@
 
 (define/contract (write this x)
   ((or/c string? isBuffer? input-port?) . ->m . void?)
-  (push-field! byte-strings this
+  (push-field! ref-byte-strings this
                (let loop ([x x])
                  (cond
                    [(isBuffer? x) x]
                    [(input-port? x) (loop (port->bytes x))]
                    [else (bytes-append (newBuffer x) #"\n")]))))
 
-(define got-byte-strings? pair?)
+(define got-ref-byte-strings? pair?)
 
 (define/contract (end this [chunk #f])
   (() ((or/c string? isBuffer? input-port?)) . ->*m . void?)
@@ -40,16 +40,16 @@
 
   #;(report* 'end! (· this id))
   (define bstrs-to-write
-    (let ([current-bstrs (reverse (· this byte-strings))])
+    (let ([current-bstrs (reverse (· this ref-byte-strings))])
       (if (and (compress-streams?)
                (not (hash-ref (· this payload) 'Filter #f))
-               (got-byte-strings? current-bstrs))
+               (got-ref-byte-strings? current-bstrs))
           (let ([deflated-chunk (deflate (apply bytes-append current-bstrs))])
             (hash-set! (· this payload) 'Filter "FlateDecode")
             (list deflated-chunk))
           current-bstrs)))
   
-  (when (got-byte-strings? bstrs-to-write)
+  (when (got-ref-byte-strings? bstrs-to-write)
     (hash-set! (· this payload) 'Length (apply + (map buffer-length bstrs-to-write))))
 
   (define this-doc (· this document)) 
@@ -58,7 +58,7 @@
   (with-method ([doc_write (this-doc write)])
     (doc_write (format "~a 0 obj" (· this id)))
     (doc_write (convert (· this payload)))
-    (when (got-byte-strings? bstrs-to-write)
+    (when (got-ref-byte-strings? bstrs-to-write)
       (doc_write "stream")
       (for ([bstr (in-list bstrs-to-write)])
         (doc_write bstr))