diff --git a/lib/encoding.js b/lib/encoding.js
index c8389cc..0082d8f 100644
--- a/lib/encoding.js
+++ b/lib/encoding.js
@@ -582,6 +582,7 @@
    * @param {{fatal: boolean}} options
    */
   function UTF8Encoder(options) {
+    var fatal = options.fatal;
     /**
      * @param {Stream} stream Input stream.
      * @param {number} code_point Next code point read from the stream.
diff --git a/lib/encoding.cjs.js b/lib/encoding.lib.js
similarity index 100%
rename from lib/encoding.cjs.js
rename to lib/encoding.lib.js
diff --git a/lib/encoding.lib.mjs b/lib/encoding.lib.mjs
new file mode 100644
index 0000000..79e8ddd
--- /dev/null
+++ b/lib/encoding.lib.mjs
@@ -0,0 +1,665 @@
+'use strict';
+
+// This is free and unencumbered software released into the public domain.
+// See LICENSE.md for more information.
+
+//
+// Utilities
+//
+
+/**
+ * @param {number} a The number to test.
+ * @param {number} min The minimum value in the range, inclusive.
+ * @param {number} max The maximum value in the range, inclusive.
+ * @return {boolean} True if a >= min and a <= max.
+ */
+function inRange(a, min, max) {
+  return min <= a && a <= max;
+}
+
+/**
+ * @param {*} o
+ * @return {Object}
+ */
+function ToDictionary(o) {
+  if (o === undefined) return {};
+  if (o === Object(o)) return o;
+  throw TypeError('Could not convert argument to dictionary');
+}
+
+/**
+ * @param {string} string Input string of UTF-16 code units.
+ * @return {!Array.<number>} Code points.
+ */
+function stringToCodePoints(string) {
+  // https://heycam.github.io/webidl/#dfn-obtain-unicode
+
+  // 1. Let S be the DOMString value.
+  var s = String(string);
+
+  // 2. Let n be the length of S.
+  var n = s.length;
+
+  // 3. Initialize i to 0.
+  var i = 0;
+
+  // 4. Initialize U to be an empty sequence of Unicode characters.
+  var u = [];
+
+  // 5. While i < n:
+  while (i < n) {
+
+    // 1. Let c be the code unit in S at index i.
+    var c = s.charCodeAt(i);
+
+    // 2. Depending on the value of c:
+
+    // c < 0xD800 or c > 0xDFFF
+    if (c < 0xD800 || c > 0xDFFF) {
+      // Append to U the Unicode character with code point c.
+      u.push(c);
+    }
+
+    // 0xDC00 ≤ c ≤ 0xDFFF
+    else if (0xDC00 <= c && c <= 0xDFFF) {
+      // Append to U a U+FFFD REPLACEMENT CHARACTER.
+      u.push(0xFFFD);
+    }
+
+    // 0xD800 ≤ c ≤ 0xDBFF
+    else if (0xD800 <= c && c <= 0xDBFF) {
+      // 1. If i = n−1, then append to U a U+FFFD REPLACEMENT
+      // CHARACTER.
+      if (i === n - 1) {
+        u.push(0xFFFD);
+      }
+      // 2. Otherwise, i < n−1:
+      else {
+        // 1. Let d be the code unit in S at index i+1.
+        var d = string.charCodeAt(i + 1);
+
+        // 2. If 0xDC00 ≤ d ≤ 0xDFFF, then:
+        if (0xDC00 <= d && d <= 0xDFFF) {
+          // 1. Let a be c & 0x3FF.
+          var a = c & 0x3FF;
+
+          // 2. Let b be d & 0x3FF.
+          var b = d & 0x3FF;
+
+          // 3. Append to U the Unicode character with code point
+          // 2^16+2^10*a+b.
+          u.push(0x10000 + (a << 10) + b);
+
+          // 4. Set i to i+1.
+          i += 1;
+        }
+
+        // 3. Otherwise, d < 0xDC00 or d > 0xDFFF. Append to U a
+        // U+FFFD REPLACEMENT CHARACTER.
+        else  {
+          u.push(0xFFFD);
+        }
+      }
+    }
+
+    // 3. Set i to i+1.
+    i += 1;
+  }
+
+  // 6. Return U.
+  return u;
+}
+
+/**
+ * @param {!Array.<number>} code_points Array of code points.
+ * @return {string} string String of UTF-16 code units.
+ */
+function codePointsToString(code_points) {
+  var s = '';
+  for (var i = 0; i < code_points.length; ++i) {
+    var cp = code_points[i];
+    if (cp <= 0xFFFF) {
+      s += String.fromCharCode(cp);
+    } else {
+      cp -= 0x10000;
+      s += String.fromCharCode((cp >> 10) + 0xD800,
+                               (cp & 0x3FF) + 0xDC00);
+    }
+  }
+  return s;
+}
+
+
+//
+// Implementation of Encoding specification
+// https://encoding.spec.whatwg.org/
+//
+
+//
+// 3. Terminology
+//
+
+/**
+ * End-of-stream is a special token that signifies no more tokens
+ * are in the stream.
+ * @const
+ */ var end_of_stream = -1;
+
+/**
+ * A stream represents an ordered sequence of tokens.
+ *
+ * @constructor
+ * @param {!(Array.<number>|Uint8Array)} tokens Array of tokens that provide the
+ * stream.
+ */
+function Stream(tokens) {
+  /** @type {!Array.<number>} */
+  this.tokens = [].slice.call(tokens);
+}
+
+Stream.prototype = {
+  /**
+   * @return {boolean} True if end-of-stream has been hit.
+   */
+  endOfStream: function() {
+    return !this.tokens.length;
+  },
+
+  /**
+   * When a token is read from a stream, the first token in the
+   * stream must be returned and subsequently removed, and
+   * end-of-stream must be returned otherwise.
+   *
+   * @return {number} Get the next token from the stream, or
+   * end_of_stream.
+   */
+   read: function() {
+    if (!this.tokens.length)
+      return end_of_stream;
+     return this.tokens.shift();
+   },
+
+  /**
+   * When one or more tokens are prepended to a stream, those tokens
+   * must be inserted, in given order, before the first token in the
+   * stream.
+   *
+   * @param {(number|!Array.<number>)} token The token(s) to prepend to the stream.
+   */
+  prepend: function(token) {
+    if (Array.isArray(token)) {
+      var tokens = /**@type {!Array.<number>}*/(token);
+      while (tokens.length)
+        this.tokens.unshift(tokens.pop());
+    } else {
+      this.tokens.unshift(token);
+    }
+  },
+
+  /**
+   * When one or more tokens are pushed to a stream, those tokens
+   * must be inserted, in given order, after the last token in the
+   * stream.
+   *
+   * @param {(number|!Array.<number>)} token The tokens(s) to prepend to the stream.
+   */
+  push: function(token) {
+    if (Array.isArray(token)) {
+      var tokens = /**@type {!Array.<number>}*/(token);
+      while (tokens.length)
+        this.tokens.push(tokens.shift());
+    } else {
+      this.tokens.push(token);
+    }
+  }
+};
+
+//
+// 4. Encodings
+//
+
+// 4.1 Encoders and decoders
+
+/** @const */
+var finished = -1;
+
+/**
+ * @param {boolean} fatal If true, decoding errors raise an exception.
+ * @param {number=} opt_code_point Override the standard fallback code point.
+ * @return {number} The code point to insert on a decoding error.
+ */
+function decoderError(fatal, opt_code_point) {
+  if (fatal)
+    throw TypeError('Decoder error');
+  return opt_code_point || 0xFFFD;
+}
+
+/** @interface */
+function Decoder() {}
+Decoder.prototype = {
+  /**
+   * @param {Stream} stream The stream of bytes being decoded.
+   * @param {number} bite The next byte read from the stream.
+   * @return {?(number|!Array.<number>)} The next code point(s)
+   *     decoded, or null if not enough data exists in the input
+   *     stream to decode a complete code point, or |finished|.
+   */
+  handler: function(stream, bite) {}
+};
+
+/** @interface */
+function Encoder() {}
+Encoder.prototype = {
+  /**
+   * @param {Stream} stream The stream of code points being encoded.
+   * @param {number} code_point Next code point read from the stream.
+   * @return {(number|!Array.<number>)} Byte(s) to emit, or |finished|.
+   */
+  handler: function(stream, code_point) {}
+};
+
+//
+// 7. API
+//
+
+/** @const */ var DEFAULT_ENCODING = 'utf-8';
+
+// 7.1 Interface TextDecoder
+
+/**
+ * @constructor
+ * @param {string=} encoding The label of the encoding;
+ *     defaults to 'utf-8'.
+ * @param {Object=} options
+ */
+function TextDecoder(encoding, options) {
+  if (!(this instanceof TextDecoder)) {
+    return new TextDecoder(encoding, options);
+  }
+  encoding = encoding !== undefined ? String(encoding).toLowerCase() : DEFAULT_ENCODING;
+  if (encoding !== DEFAULT_ENCODING) {
+    throw new Error('Encoding not supported. Only utf-8 is supported');
+  }
+  options = ToDictionary(options);
+
+  /** @private @type {boolean} */
+  this._streaming = false;
+  /** @private @type {boolean} */
+  this._BOMseen = false;
+  /** @private @type {?Decoder} */
+  this._decoder = null;
+  /** @private @type {boolean} */
+  this._fatal = Boolean(options['fatal']);
+  /** @private @type {boolean} */
+  this._ignoreBOM = Boolean(options['ignoreBOM']);
+
+  Object.defineProperty(this, 'encoding', {value: 'utf-8'});
+  Object.defineProperty(this, 'fatal', {value: this._fatal});
+  Object.defineProperty(this, 'ignoreBOM', {value: this._ignoreBOM});
+}
+
+TextDecoder.prototype = {
+  /**
+   * @param {ArrayBufferView=} input The buffer of bytes to decode.
+   * @param {Object=} options
+   * @return {string} The decoded string.
+   */
+  decode: function decode(input, options) {
+    var bytes;
+    if (typeof input === 'object' && input instanceof ArrayBuffer) {
+      bytes = new Uint8Array(input);
+    } else if (typeof input === 'object' && 'buffer' in input &&
+               input.buffer instanceof ArrayBuffer) {
+      bytes = new Uint8Array(input.buffer,
+                             input.byteOffset,
+                             input.byteLength);
+    } else {
+      bytes = new Uint8Array(0);
+    }
+
+    options = ToDictionary(options);
+
+    if (!this._streaming) {
+      this._decoder = new UTF8Decoder({fatal: this._fatal});
+      this._BOMseen = false;
+    }
+    this._streaming = Boolean(options['stream']);
+
+    var input_stream = new Stream(bytes);
+
+    var code_points = [];
+
+    /** @type {?(number|!Array.<number>)} */
+    var result;
+
+    while (!input_stream.endOfStream()) {
+      result = this._decoder.handler(input_stream, input_stream.read());
+      if (result === finished)
+        break;
+      if (result === null)
+        continue;
+      if (Array.isArray(result))
+        code_points.push.apply(code_points, /**@type {!Array.<number>}*/(result));
+      else
+        code_points.push(result);
+    }
+    if (!this._streaming) {
+      do {
+        result = this._decoder.handler(input_stream, input_stream.read());
+        if (result === finished)
+          break;
+        if (result === null)
+          continue;
+        if (Array.isArray(result))
+          code_points.push.apply(code_points, /**@type {!Array.<number>}*/(result));
+        else
+          code_points.push(result);
+      } while (!input_stream.endOfStream());
+      this._decoder = null;
+    }
+
+    if (code_points.length) {
+      // If encoding is one of utf-8, utf-16be, and utf-16le, and
+      // ignore BOM flag and BOM seen flag are unset, run these
+      // subsubsteps:
+      if (['utf-8'].indexOf(this.encoding) !== -1 &&
+          !this._ignoreBOM && !this._BOMseen) {
+        // If token is U+FEFF, set BOM seen flag.
+        if (code_points[0] === 0xFEFF) {
+          this._BOMseen = true;
+          code_points.shift();
+        } else {
+          // Otherwise, if token is not end-of-stream, set BOM seen
+          // flag and append token to output.
+          this._BOMseen = true;
+        }
+      }
+    }
+
+    return codePointsToString(code_points);
+  }
+};
+
+// 7.2 Interface TextEncoder
+
+/**
+ * @constructor
+ * @param {string=} encoding The label of the encoding;
+ *     defaults to 'utf-8'.
+ * @param {Object=} options
+ */
+function TextEncoder(encoding, options) {
+  if (!(this instanceof TextEncoder))
+    return new TextEncoder(encoding, options);
+  encoding = encoding !== undefined ? String(encoding).toLowerCase() : DEFAULT_ENCODING;
+  if (encoding !== DEFAULT_ENCODING) {
+    throw new Error('Encoding not supported. Only utf-8 is supported');
+  }
+  options = ToDictionary(options);
+
+  /** @private @type {boolean} */
+  this._streaming = false;
+  /** @private @type {?Encoder} */
+  this._encoder = null;
+  /** @private @type {{fatal: boolean}} */
+  this._options = {fatal: Boolean(options['fatal'])};
+
+  Object.defineProperty(this, 'encoding', {value: 'utf-8'});
+}
+
+TextEncoder.prototype = {
+  /**
+   * @param {string=} opt_string The string to encode.
+   * @param {Object=} options
+   * @return {Uint8Array} Encoded bytes, as a Uint8Array.
+   */
+  encode: function encode(opt_string, options) {
+    opt_string = opt_string ? String(opt_string) : '';
+    options = ToDictionary(options);
+
+    // NOTE: This option is nonstandard. None of the encodings
+    // permitted for encoding (i.e. UTF-8, UTF-16) are stateful,
+    // so streaming is not necessary.
+    if (!this._streaming)
+      this._encoder = new UTF8Encoder(this._options);
+    this._streaming = Boolean(options['stream']);
+
+    var bytes = [];
+    var input_stream = new Stream(stringToCodePoints(opt_string));
+    /** @type {?(number|!Array.<number>)} */
+    var result;
+    while (!input_stream.endOfStream()) {
+      result = this._encoder.handler(input_stream, input_stream.read());
+      if (result === finished)
+        break;
+      if (Array.isArray(result))
+        bytes.push.apply(bytes, /**@type {!Array.<number>}*/(result));
+      else
+        bytes.push(result);
+    }
+    if (!this._streaming) {
+      while (true) {
+        result = this._encoder.handler(input_stream, input_stream.read());
+        if (result === finished)
+          break;
+        if (Array.isArray(result))
+          bytes.push.apply(bytes, /**@type {!Array.<number>}*/(result));
+        else
+          bytes.push(result);
+      }
+      this._encoder = null;
+    }
+    return new Uint8Array(bytes);
+  }
+};
+
+//
+// 8. The encoding
+//
+
+// 8.1 utf-8
+
+/**
+ * @constructor
+ * @implements {Decoder}
+ * @param {{fatal: boolean}} options
+ */
+function UTF8Decoder(options) {
+  var fatal = options.fatal;
+
+  // utf-8's decoder's has an associated utf-8 code point, utf-8
+  // bytes seen, and utf-8 bytes needed (all initially 0), a utf-8
+  // lower boundary (initially 0x80), and a utf-8 upper boundary
+  // (initially 0xBF).
+  var /** @type {number} */ utf8_code_point = 0,
+      /** @type {number} */ utf8_bytes_seen = 0,
+      /** @type {number} */ utf8_bytes_needed = 0,
+      /** @type {number} */ utf8_lower_boundary = 0x80,
+      /** @type {number} */ utf8_upper_boundary = 0xBF;
+
+  /**
+   * @param {Stream} stream The stream of bytes being decoded.
+   * @param {number} bite The next byte read from the stream.
+   * @return {?(number|!Array.<number>)} The next code point(s)
+   *     decoded, or null if not enough data exists in the input
+   *     stream to decode a complete code point.
+   */
+  this.handler = function(stream, bite) {
+    // 1. If byte is end-of-stream and utf-8 bytes needed is not 0,
+    // set utf-8 bytes needed to 0 and return error.
+    if (bite === end_of_stream && utf8_bytes_needed !== 0) {
+      utf8_bytes_needed = 0;
+      return decoderError(fatal);
+    }
+
+    // 2. If byte is end-of-stream, return finished.
+    if (bite === end_of_stream)
+      return finished;
+
+    // 3. If utf-8 bytes needed is 0, based on byte:
+    if (utf8_bytes_needed === 0) {
+
+      // 0x00 to 0x7F
+      if (inRange(bite, 0x00, 0x7F)) {
+        // Return a code point whose value is byte.
+        return bite;
+      }
+
+      // 0xC2 to 0xDF
+      if (inRange(bite, 0xC2, 0xDF)) {
+        // Set utf-8 bytes needed to 1 and utf-8 code point to byte
+        // − 0xC0.
+        utf8_bytes_needed = 1;
+        utf8_code_point = bite - 0xC0;
+      }
+
+      // 0xE0 to 0xEF
+      else if (inRange(bite, 0xE0, 0xEF)) {
+        // 1. If byte is 0xE0, set utf-8 lower boundary to 0xA0.
+        if (bite === 0xE0)
+          utf8_lower_boundary = 0xA0;
+        // 2. If byte is 0xED, set utf-8 upper boundary to 0x9F.
+        if (bite === 0xED)
+          utf8_upper_boundary = 0x9F;
+        // 3. Set utf-8 bytes needed to 2 and utf-8 code point to
+        // byte − 0xE0.
+        utf8_bytes_needed = 2;
+        utf8_code_point = bite - 0xE0;
+      }
+
+      // 0xF0 to 0xF4
+      else if (inRange(bite, 0xF0, 0xF4)) {
+        // 1. If byte is 0xF0, set utf-8 lower boundary to 0x90.
+        if (bite === 0xF0)
+          utf8_lower_boundary = 0x90;
+        // 2. If byte is 0xF4, set utf-8 upper boundary to 0x8F.
+        if (bite === 0xF4)
+          utf8_upper_boundary = 0x8F;
+        // 3. Set utf-8 bytes needed to 3 and utf-8 code point to
+        // byte − 0xF0.
+        utf8_bytes_needed = 3;
+        utf8_code_point = bite - 0xF0;
+      }
+
+      // Otherwise
+      else {
+        // Return error.
+        return decoderError(fatal);
+      }
+
+      // Then (byte is in the range 0xC2 to 0xF4) set utf-8 code
+      // point to utf-8 code point << (6 × utf-8 bytes needed) and
+      // return continue.
+      utf8_code_point = utf8_code_point << (6 * utf8_bytes_needed);
+      return null;
+    }
+
+    // 4. If byte is not in the range utf-8 lower boundary to utf-8
+    // upper boundary, run these substeps:
+    if (!inRange(bite, utf8_lower_boundary, utf8_upper_boundary)) {
+
+      // 1. Set utf-8 code point, utf-8 bytes needed, and utf-8
+      // bytes seen to 0, set utf-8 lower boundary to 0x80, and set
+      // utf-8 upper boundary to 0xBF.
+      utf8_code_point = utf8_bytes_needed = utf8_bytes_seen = 0;
+      utf8_lower_boundary = 0x80;
+      utf8_upper_boundary = 0xBF;
+
+      // 2. Prepend byte to stream.
+      stream.prepend(bite);
+
+      // 3. Return error.
+      return decoderError(fatal);
+    }
+
+    // 5. Set utf-8 lower boundary to 0x80 and utf-8 upper boundary
+    // to 0xBF.
+    utf8_lower_boundary = 0x80;
+    utf8_upper_boundary = 0xBF;
+
+    // 6. Increase utf-8 bytes seen by one and set utf-8 code point
+    // to utf-8 code point + (byte − 0x80) << (6 × (utf-8 bytes
+    // needed − utf-8 bytes seen)).
+    utf8_bytes_seen += 1;
+    utf8_code_point += (bite - 0x80) << (6 * (utf8_bytes_needed - utf8_bytes_seen));
+
+    // 7. If utf-8 bytes seen is not equal to utf-8 bytes needed,
+    // continue.
+    if (utf8_bytes_seen !== utf8_bytes_needed)
+      return null;
+
+    // 8. Let code point be utf-8 code point.
+    var code_point = utf8_code_point;
+
+    // 9. Set utf-8 code point, utf-8 bytes needed, and utf-8 bytes
+    // seen to 0.
+    utf8_code_point = utf8_bytes_needed = utf8_bytes_seen = 0;
+
+    // 10. Return a code point whose value is code point.
+    return code_point;
+  };
+}
+
+/**
+ * @constructor
+ * @implements {Encoder}
+ * @param {{fatal: boolean}} options
+ */
+function UTF8Encoder(options) {
+  var fatal = options.fatal;
+  /**
+   * @param {Stream} stream Input stream.
+   * @param {number} code_point Next code point read from the stream.
+   * @return {(number|!Array.<number>)} Byte(s) to emit.
+   */
+  this.handler = function(stream, code_point) {
+    // 1. If code point is end-of-stream, return finished.
+    if (code_point === end_of_stream)
+      return finished;
+
+    // 2. If code point is in the range U+0000 to U+007F, return a
+    // byte whose value is code point.
+    if (inRange(code_point, 0x0000, 0x007f))
+      return code_point;
+
+    // 3. Set count and offset based on the range code point is in:
+    var count, offset;
+    // U+0080 to U+07FF:    1 and 0xC0
+    if (inRange(code_point, 0x0080, 0x07FF)) {
+      count = 1;
+      offset = 0xC0;
+    }
+    // U+0800 to U+FFFF:    2 and 0xE0
+    else if (inRange(code_point, 0x0800, 0xFFFF)) {
+      count = 2;
+      offset = 0xE0;
+    }
+    // U+10000 to U+10FFFF: 3 and 0xF0
+    else if (inRange(code_point, 0x10000, 0x10FFFF)) {
+      count = 3;
+      offset = 0xF0;
+    }
+
+    // 4.Let bytes be a byte sequence whose first byte is (code
+    // point >> (6 × count)) + offset.
+    var bytes = [(code_point >> (6 * count)) + offset];
+
+    // 5. Run these substeps while count is greater than 0:
+    while (count > 0) {
+
+      // 1. Set temp to code point >> (6 × (count − 1)).
+      var temp = code_point >> (6 * (count - 1));
+
+      // 2. Append to bytes 0x80 | (temp & 0x3F).
+      bytes.push(0x80 | (temp & 0x3F));
+
+      // 3. Decrease count by one.
+      count -= 1;
+    }
+
+    // 6. Return bytes bytes, in order.
+    return bytes;
+  };
+}
+
+export {TextEncoder, TextDecoder};
diff --git a/package.json b/package.json
index 06bab4b..c7de3fd 100644
--- a/package.json
+++ b/package.json
@@ -5,13 +5,13 @@
     "Rick Eyre <rick.eyre@outlook.com>",
     "Joshua Bell <inexorabletash@gmail.com>"
   ],
-  "version": "1.0.0",
+  "version": "1.0.1",
   "description": "UTF-8 only polyfill for the Encoding Living Standard's API.",
-  "main": "lib/encoding.cjs.js",
+  "main": "lib/encoding.lib",
   "jsnext:main": "src/encoding.js",
   "files": [
     "src",
-    "dist"
+    "lib"
   ],
   "repository": {
     "type": "git",
@@ -27,7 +27,7 @@
   },
   "homepage": "https://github.com/arv/text-encoding-utf-8",
   "scripts": {
-    "prepublish": "rollup -f iife -o lib/encoding.js -- src/polyfill.js && rollup -f cjs -o lib/encoding.cjs.js -- src/encoding.js"
+    "prepublish": "rollup -f iife -o lib/encoding.js -- src/polyfill.js && rollup -f cjs -o lib/encoding.lib.js -- src/encoding.js && cp src/encoding.js lib/encoding.lib.mjs"
   },
   "devDependencies": {
     "rollup": "^0.21.0"