diff --git a/xenomorph/xenomorph/base.rkt b/xenomorph/xenomorph/base.rkt
index d04088fc..c790784f 100644
--- a/xenomorph/xenomorph/base.rkt
+++ b/xenomorph/xenomorph/base.rkt
@@ -58,7 +58,7 @@ We don't make port-arg the last arg (similar to other Racket port funcs) because
   (unless port-arg (get-output-bytes port)))
                                       
 (define (size xo [val #f] #:parent [parent #f] . args)
-  (send xo x:size (and val (send xo pre-encode val)) parent . args))
+  (send xo x:size val parent . args))
 
 (define (xenomorphic-type? x) (is-a? x x:base%))
 (define xenomorphic? xenomorphic-type?)
diff --git a/xenomorph/xenomorph/scribblings/xenomorph.scrbl b/xenomorph/xenomorph/scribblings/xenomorph.scrbl
index 6e8e7024..6f50b122 100644
--- a/xenomorph/xenomorph/scribblings/xenomorph.scrbl
+++ b/xenomorph/xenomorph/scribblings/xenomorph.scrbl
@@ -308,16 +308,6 @@ If @racket[byte-dest] is an @racket[output-port?], the bytes are written there a
 If @racket[val] does not match the @racket[xenomorphic-obj] type appropriately — for instance, you try to @racket[encode] a negative integer using an unsigned integer type like @racket[uint8] — then an error will arise.
 }
 
-@defproc[
-(size
-[xenomorphic-obj xenomorphic?]
-[val any/c #false]
-[#:parent parent (or/c xenomorphic? #false) #false]
-[arg any/c] ...)
-exact-nonnegative-integer?]{
-The length of the @tech{byte string} that @racket[val] would produce if it were encoded using @racket[encode].
-}
-
 
 @section{Core xenomorphic objects}
 
diff --git a/xenomorph/xenomorph/test/api-test.rkt b/xenomorph/xenomorph/test/api-test.rkt
new file mode 100644
index 00000000..052929b9
--- /dev/null
+++ b/xenomorph/xenomorph/test/api-test.rkt
@@ -0,0 +1,43 @@
+#lang br
+(require xenomorph rackunit)
+
+(define-simple-check (check-xenomorphic type val)
+  (let ([de (decode type (encode type val #f))])
+    (if (flonum? val)
+        (check-= de val 0.01)
+        (check-equal? de val))))
+
+(define bigint (x:string #:pre-encode number->string
+                         #:post-decode string->number))
+
+(check-xenomorphic bigint 1234567890987654321)
+
+(define exact (x:list #:type bigint
+                      #:length 2
+                      #:pre-encode (λ (x) (list (numerator x) (denominator x)))
+                      #:post-decode (λ (nd) (apply / nd))))
+
+(check-xenomorphic exact 12345678/8765)
+
+(define real (x:versioned-dict
+              #:type uint8
+              #:version-key 'version
+              #:versions
+              (list
+               (cons 0 (list (cons 'val exact)))
+               (cons 1 (list (cons 'val float))))
+              #:pre-encode (λ (num) (list (cons 'val num)
+                                          (cons 'version (if (exact? num)
+                                                             0
+                                                             1))))
+              #:post-decode (λ (h) (hash-ref h 'val))))
+
+(require math)
+(check-xenomorphic real pi)
+
+(define complex (x:list #:type real
+                        #:length 2
+                        #:pre-encode (λ (num) (list (real-part num) (imag-part num)))
+                        #:post-decode (λ (ri) (+ (first ri) (* 0+1i (second ri))))))
+
+(check-xenomorphic complex 3/4+5i)
diff --git a/xenomorph/xenomorph/test/main.rkt b/xenomorph/xenomorph/test/main.rkt
index 058f2987..57861dd2 100644
--- a/xenomorph/xenomorph/test/main.rkt
+++ b/xenomorph/xenomorph/test/main.rkt
@@ -13,4 +13,5 @@
          "string-test.rkt"
          "symbol-test.rkt"
          "vector-test.rkt"
-         "versioned-dict-test.rkt")
+         "versioned-dict-test.rkt"
+         "api-test.rkt")