diff --git a/README.md b/README.md
index 35fad70..e893976 100644
--- a/README.md
+++ b/README.md
@@ -54,7 +54,7 @@ The [OCapN](https://ocapn.org/) network protocol treats strings and byte-arrays
 ## Solution
 
 This proposal introduces additional methods and read-only accessor properties to `ArrayBuffer.prototype` that fit naturally into those explained above. Just as a buffer can be resizable or not, and detached or not, this proposal enables buffers to be immutable or not. Just as `transferToFixedSize` moves the contents of a original buffer into a newly created non-resizable buffer, this proposal provides a transfer operation that moves the contents of an original original buffer into a newly created immutable buffer. Altogether, this proposal only adds to `ArrayBuffer.prototype` one method
-- `transferToImmutable() :ArrayBuffer` -- move the contents of the original buffer into a new immutable buffer, detach the original buffer, and return the new buffer.
+- `transferToImmutable(newByteLength?: number) :ArrayBuffer` -- move the contents of the original buffer into a new immutable buffer, detach the original buffer, and return the new buffer.
 
 and one read-only accessor
 - `immutable: boolean` -- is this buffer immutable, or can its contents be changed?
@@ -131,15 +131,6 @@ No, TypedArray index properties should continue to track the state of the underl
 </dd>
 
 
-<dt>
-
-Should `transferToImmutable` support a `newByteLength` argument?
-</dt>
-<dd>
-https://github.com/tc39/proposal-immutable-arraybuffer/issues/15
-</dd>
-
-
 <dt>
 
 Should ArrayBuffers support zero-copy slices (e.g., `arrayBuffer.sliceToImmutable()`)?
diff --git a/spec.emu b/spec.emu
index b8b6332..3f98c05 100644
--- a/spec.emu
+++ b/spec.emu
@@ -637,11 +637,11 @@ contributors: Mark S. Miller, Richard Gibson
       <ins class="block">
 
         <emu-clause id="sec-arraybuffer.prototype.transfertoimmutable">
-          <h1>ArrayBuffer.prototype.transferToImmutable ( )</h1>
+          <h1>ArrayBuffer.prototype.transferToImmutable ( [ _newLength_ ] )</h1>
           <p>This method performs the following steps when called:</p>
           <emu-alg>
             1. Let _O_ be the *this* value.
-            1. Return ? ArrayBufferCopyAndDetach(_O_, *undefined*, ~immutable~).
+            1. Return ? ArrayBufferCopyAndDetach(_O_, _newLength_, ~immutable~).
           </emu-alg>
         </emu-clause>
       </ins>