diff --git a/README.md b/README.md
index ff1dcac..1d44c68 100644
--- a/README.md
+++ b/README.md
@@ -42,11 +42,11 @@ The hex methods do not take any options.
 
 ## Writing to an existing Uint8Array
 
-The `Uint8Array.fromBase64Into` method allows writing to an existing Uint8Array. Like the [TextEncoder `encodeInto` method](https://developer.mozilla.org/en-US/docs/Web/API/TextEncoder/encodeInto), it returns a `{ read, written }` pair.
+The `Uint8Array.prototype.setFromBase64` method allows writing to an existing Uint8Array. Like the [TextEncoder `encodeInto` method](https://developer.mozilla.org/en-US/docs/Web/API/TextEncoder/encodeInto), it returns a `{ read, written }` pair.
 
 ```js
 let target = new Uint8Array(8);
-let { read, written } = Uint8Array.fromBase64Into('Zm9vYmFy', target);
+let { read, written } = target.setFromBase64('Zm9vYmFy');
 assert.deepStrictEqual([...target], [102, 111, 111, 98, 97, 114, 0, 0]);
 assert.deepStrictEqual({ read, written }, { read: 8, written: 6 });
 ```
@@ -55,7 +55,7 @@ This method takes an optional final options bag with the same options as above.
 
 As with `encodeInto`, there is not explicit support for writing to specified offset of the target, but you can accomplish that by creating a subarray.
 
-`Uint8Array.fromHexInto` is the same except for hex.
+`Uint8Array.prototype.setFromHex` is the same except for hex.
 
 ## Streaming
 
diff --git a/playground/index-raw.html b/playground/index-raw.html
index b165318..f8dfa3e 100644
--- a/playground/index-raw.html
+++ b/playground/index-raw.html
@@ -112,22 +112,22 @@ <h3>Options</h3>
 </code></pre>
 
 <h3>Writing to an existing Uint8Array</h3>
-<p>The <code>Uint8Array.fromBase64Into</code> method allows writing to an existing Uint8Array. Like the <a href="https://developer.mozilla.org/en-US/docs/Web/API/TextEncoder/encodeInto">TextEncoder <code>encodeInto</code> method</a>, it returns a <code>{ read, written }</code> pair.</p>
+<p>The <code>Uint8Array.prototype.setFromBase64</code> method allows writing to an existing Uint8Array. Like the <a href="https://developer.mozilla.org/en-US/docs/Web/API/TextEncoder/encodeInto">TextEncoder <code>encodeInto</code> method</a>, it returns a <code>{ read, written }</code> pair.</p>
 
 <p>This method takes an optional final options bag with the same options as above.</p>
 
 <pre class="language-js"><code class="language-js">
 let target = new Uint8Array(7);
-let { read, written } = Uint8Array.fromBase64Into('Zm9vYmFy', target);
+let { read, written } = target.setFromBase64('Zm9vYmFy');
 console.log({ target, read, written });
 // { target: Uint8Array([102, 111, 111, 98, 97, 114, 0]), read: 8, written: 6 }
 </code></pre>
 
-<p><code>Uint8Array.fromHexInto</code> is the same except for hex.</p>
+<p><code>Uint8Array.prototype.setFromHex</code> is the same except for hex.</p>
 
 <pre class="language-js"><code class="language-js">
 let target = new Uint8Array(6);
-let { read, written } = Uint8Array.fromHexInto('deadbeef', target);
+let { read, written } = target.setFromHex('deadbeef');
 console.log({ target, read, written });
 // { target: Uint8Array([222, 173, 190, 239, 0, 0]), read: 8, written: 4 }
 </code></pre>
diff --git a/playground/polyfill-install.mjs b/playground/polyfill-install.mjs
index f7300bf..ad356ca 100644
--- a/playground/polyfill-install.mjs
+++ b/playground/polyfill-install.mjs
@@ -19,17 +19,19 @@ Object.defineProperty(Uint8Array, 'fromBase64', { enumerable: false });
 Object.defineProperty(Uint8Array.fromBase64, 'length', { value: 1 });
 Object.defineProperty(Uint8Array.fromBase64, 'name', { value: 'fromBase64' });
 
-Uint8Array.fromBase64Into = (string, into, options) => {
-  if (typeof string !== 'string') {
-    throw new TypeError('expected input to be a string');
+// method shenanigans to make a non-constructor which can refer to "this"
+Uint8Array.prototype.setFromBase64 = {
+  setFromBase64(string, options) {
+    checkUint8Array(this);
+    if (typeof string !== 'string') {
+      throw new TypeError('expected input to be a string');
+    }
+    let { read, bytes } = base64ToUint8Array(string, options, this);
+    return { read, written: bytes.length };
   }
-  checkUint8Array(into);
-  let { read, bytes } = base64ToUint8Array(string, options, into);
-  return { read, written: bytes.length };
-};
-Object.defineProperty(Uint8Array, 'fromBase64Into', { enumerable: false });
-Object.defineProperty(Uint8Array.fromBase64Into, 'length', { value: 2 });
-Object.defineProperty(Uint8Array.fromBase64Into, 'name', { value: 'fromBase64Into' });
+}.setFromBase64;
+Object.defineProperty(Uint8Array.prototype, 'setFromBase64', { enumerable: false });
+Object.defineProperty(Uint8Array.prototype.setFromBase64, 'length', { value: 1 });
 
 Uint8Array.prototype.toHex = {
   toHex() {
@@ -47,13 +49,14 @@ Uint8Array.fromHex = (string) => {
 Object.defineProperty(Uint8Array, 'fromHex', { enumerable: false });
 Object.defineProperty(Uint8Array.fromHex, 'name', { value: 'fromHex' });
 
-Uint8Array.fromHexInto = (string, into) => {
-  if (typeof string !== 'string') {
-    throw new TypeError('expected input to be a string');
+Uint8Array.prototype.setFromHex = {
+  setFromHex(string) {
+    checkUint8Array(this);
+    if (typeof string !== 'string') {
+      throw new TypeError('expected input to be a string');
+    }
+    let { read, bytes } = hexToUint8Array(string, this);
+    return { read, written: bytes.length };
   }
-  checkUint8Array(into);
-  let { read, bytes } = hexToUint8Array(string, into);
-  return { read, written: bytes.length };
-};
-Object.defineProperty(Uint8Array, 'fromHexInto', { enumerable: false });
-Object.defineProperty(Uint8Array.fromHexInto, 'name', { value: 'fromHexInto' });
+}.setFromHex;
+Object.defineProperty(Uint8Array.prototype, 'setFromHex', { enumerable: false });
diff --git a/spec.html b/spec.html
index 7d22698..a4c176e 100644
--- a/spec.html
+++ b/spec.html
@@ -69,11 +69,12 @@ <h1>Uint8Array.fromBase64 ( _string_ [ , _options_ ] )</h1>
   </emu-alg>
 </emu-clause>
 
-<emu-clause id="sec-uint8array.frombase64into">
-  <h1>Uint8Array.fromBase64Into ( _string_, _into_ [ , _options_ ] )</h1>
+<emu-clause id="sec-uint8array.prototype.setfrombase64">
+  <h1>Uint8Array.prototype.setFromBase64 ( _string_ [ , _options_ ] )</h1>
   <emu-alg>
-    1. If _string_ is not a String, throw a *TypeError* exception.
+    1. Let _into_ be the *this* value.
     1. Perform ? ValidateUint8Array(_into_).
+    1. If _string_ is not a String, throw a *TypeError* exception.
     1. Let _opts_ be ? GetOptionsObject(_options_).
     1. Let _alphabet_ be ? Get(_opts_, *"alphabet"*).
     1. If _alphabet_ is *undefined*, set _alphabet_ to *"base64"*.
@@ -111,11 +112,12 @@ <h1>Uint8Array.fromHex ( _string_ )</h1>
   </emu-alg>
 </emu-clause>
 
-<emu-clause id="sec-uint8array.fromhexinto">
-  <h1>Uint8Array.fromHexInto ( _string_, _into_ )</h1>
+<emu-clause id="sec-uint8array.prototype.setfromhex">
+  <h1>Uint8Array.prototype.setFromHex ( _string_ )</h1>
   <emu-alg>
-    1. If _string_ is not a String, throw a *TypeError* exception.
+    1. Let _into_ be the *this* value.
     1. Perform ? ValidateUint8Array(_into_).
+    1. If _string_ is not a String, throw a *TypeError* exception.
     1. Let _taRecord_ be MakeTypedArrayWithBufferWitnessRecord(_into_, ~seq-cst~).
     1. If IsTypedArrayOutOfBounds(_taRecord_) is *true*, throw a *TypeError* exception.
     1. Let _byteLength_ be TypedArrayByteLength(_taRecord_).
diff --git a/stream.mjs b/stream.mjs
index 47cbf08..af1c8c5 100644
--- a/stream.mjs
+++ b/stream.mjs
@@ -18,7 +18,7 @@ class Base64Decoder {
     // but may be too much if there is whitespace
     // if you're really concerned about memory, a TextDecoder style API is a bad choice
     let buffer = new Uint8Array(Math.ceil(chunk.length * 3 / 4));
-    let { read, written } = Uint8Array.fromBase64Into(chunk, buffer, opts);
+    let { read, written } = buffer.setFromBase64(chunk, opts);
     buffer = buffer.subarray(0, written);
     this.#extra = chunk.slice(read);
     return buffer;
diff --git a/test-polyfill.mjs b/test-polyfill.mjs
index d509797..82f5ed6 100644
--- a/test-polyfill.mjs
+++ b/test-polyfill.mjs
@@ -96,70 +96,70 @@ test('writing to an existing buffer', async t => {
 
   await t.test('buffer exact', () => {
     let output = new Uint8Array(6);
-    let { read, written } = Uint8Array.fromBase64Into(foobarInput, output);
+    let { read, written } = output.setFromBase64(foobarInput);
     assert.deepStrictEqual([...output], foobarOutput);
     assert.deepStrictEqual({ read, written }, { read: 8, written: 6 });
   });
 
   await t.test('buffer too large', () => {
     let output = new Uint8Array(8);
-    let { read, written } = Uint8Array.fromBase64Into(foobarInput, output);
+    let { read, written } = output.setFromBase64(foobarInput);
     assert.deepStrictEqual([...output], [...foobarOutput, 0, 0]);
     assert.deepStrictEqual({ read, written }, { read: 8, written: 6 });
   });
 
   await t.test('buffer too small', () => {
     let output = new Uint8Array(5);
-    let { read, written } = Uint8Array.fromBase64Into(foobarInput, output);
+    let { read, written } = output.setFromBase64(foobarInput);
     assert.deepStrictEqual([...output], [...foobarOutput.slice(0, 3), 0, 0]);
     assert.deepStrictEqual({ read, written }, { read: 4, written: 3 });
   });
 
   await t.test('buffer exact, padded', () => {
     let output = new Uint8Array(5);
-    let { read, written } = Uint8Array.fromBase64Into(foobaInput + '=', output);
+    let { read, written } = output.setFromBase64(foobaInput + '=');
     assert.deepStrictEqual([...output], foobarOutput.slice(0, 5));
     assert.deepStrictEqual({ read, written }, { read: 8, written: 5 });
   });
 
   await t.test('buffer exact, not padded', () => {
     let output = new Uint8Array(5);
-    let { read, written } = Uint8Array.fromBase64Into(foobaInput, output);
+    let { read, written } = output.setFromBase64(foobaInput);
     assert.deepStrictEqual([...output], foobarOutput.slice(0, 5));
     assert.deepStrictEqual({ read, written }, { read: 7, written: 5 });
   });
 
   await t.test('buffer exact, padded, stop-before-partial', () => {
     let output = new Uint8Array(5);
-    let { read, written } = Uint8Array.fromBase64Into(foobaInput + '=', output, { lastChunkHandling: 'stop-before-partial' });
+    let { read, written } = output.setFromBase64(foobaInput + '=', { lastChunkHandling: 'stop-before-partial' });
     assert.deepStrictEqual([...output], foobarOutput.slice(0, 5));
     assert.deepStrictEqual({ read, written }, { read: 8, written: 5 });
   });
 
   await t.test('buffer exact, not padded, stop-before-partial', () => {
     let output = new Uint8Array(5);
-    let { read, written } = Uint8Array.fromBase64Into(foobaInput, output, { lastChunkHandling: 'stop-before-partial' });
+    let { read, written } = output.setFromBase64(foobaInput, { lastChunkHandling: 'stop-before-partial' });
     assert.deepStrictEqual([...output], [...foobarOutput.slice(0, 3), 0, 0]);
     assert.deepStrictEqual({ read, written }, { read: 4, written: 3 });
   });
 
   await t.test('buffer too small, padded', () => {
     let output = new Uint8Array(4);
-    let { read, written } = Uint8Array.fromBase64Into(foobaInput + '=', output);
+    let { read, written } = output.setFromBase64(foobaInput + '=');
     assert.deepStrictEqual([...output], [...foobarOutput.slice(0, 3), 0]);
     assert.deepStrictEqual({ read, written }, { read: 4, written: 3 });
   });
 
   await t.test('buffer too large, trailing whitespace', () => {
     let output = new Uint8Array(8);
-    let { read, written } = Uint8Array.fromBase64Into(foobarInput + ' '.repeat(10), output);
+    let { read, written } = output.setFromBase64(foobarInput + ' '.repeat(10));
     assert.deepStrictEqual([...output], [...foobarOutput, 0, 0]);
     assert.deepStrictEqual({ read, written }, { read: 18, written: 6 });
   });
 
   await t.test('buffer too large, not padded, trailing whitespace', () => {
     let output = new Uint8Array(8);
-    let { read, written } = Uint8Array.fromBase64Into(foobaInput + ' '.repeat(10), output);
+    let { read, written } = output.setFromBase64(foobaInput + ' '.repeat(10));
     assert.deepStrictEqual([...output], [...foobarOutput.slice(0, 5), 0, 0, 0]);
     assert.deepStrictEqual({ read, written }, { read: 17, written: 5 });
   });
@@ -181,7 +181,7 @@ test('stop-before-partial', async t => {
 
   await t.test('no padding, trailing whitespace', () => {
     let output = new Uint8Array(8);
-    let { read, written } = Uint8Array.fromBase64Into(foobaInput + ' '.repeat(10), output, { lastChunkHandling: 'stop-before-partial' });
+    let { read, written } = output.setFromBase64(foobaInput + ' '.repeat(10), { lastChunkHandling: 'stop-before-partial' });
     assert.deepStrictEqual([...output], [...foobarOutput.slice(0, 3), 0, 0, 0, 0, 0]);
     assert.deepStrictEqual({ read, written }, { read: 4, written: 3 });
   });
@@ -197,21 +197,21 @@ test('hex', async t => {
 
   await t.test('decode into, exact', () => {
     let output = new Uint8Array(4);
-    let { read, written } = Uint8Array.fromHexInto(encoded, output);
+    let { read, written } = output.setFromHex(encoded);
     assert.deepStrictEqual([...output], decoded);
     assert.deepStrictEqual({ read, written }, { read: 8, written: 4 });
   });
 
   await t.test('decode into, buffer too large', () => {
     let output = new Uint8Array(6);
-    let { read, written } = Uint8Array.fromHexInto(encoded, output);
+    let { read, written } = output.setFromHex(encoded);
     assert.deepStrictEqual([...output], [...decoded, 0, 0]);
     assert.deepStrictEqual({ read, written }, { read: 8, written: 4 });
   });
 
   await t.test('decode into, buffer too small', () => {
     let output = new Uint8Array(3);
-    let { read, written } = Uint8Array.fromHexInto(encoded, output);
+    let { read, written } = output.setFromHex(encoded);
     assert.deepStrictEqual([...output], decoded.slice(0, 3));
     assert.deepStrictEqual({ read, written }, { read: 6, written: 3 });
   });