diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3ebc4799933..896e327a323 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -58,6 +58,11 @@
 
 [#41653]: https://github.com/dart-lang/sdk/issues/41653
 
+#### `dart:typed_data`
+
+*   Class `BytesBuilder` originally from `dart:io` is now available
+    in `dart:typed_data`. It's still exported from `dart:io` as well.
+
 ### Tools
 
 #### dartfmt
diff --git a/sdk/lib/_internal/vm/bin/common_patch.dart b/sdk/lib/_internal/vm/bin/common_patch.dart
index 9899f2e4a5a..cd9f149e080 100644
--- a/sdk/lib/_internal/vm/bin/common_patch.dart
+++ b/sdk/lib/_internal/vm/bin/common_patch.dart
@@ -33,7 +33,7 @@ import "dart:math" show min;
 
 import "dart:nativewrappers" show NativeFieldWrapperClass1;
 
-import "dart:typed_data" show Uint8List;
+import "dart:typed_data" show Uint8List, BytesBuilder;
 
 /// These are the additional parts of this patch library:
 // part "directory_patch.dart";
diff --git a/sdk/lib/internal/bytes_builder.dart b/sdk/lib/internal/bytes_builder.dart
new file mode 100644
index 00000000000..ea195764d10
--- /dev/null
+++ b/sdk/lib/internal/bytes_builder.dart
@@ -0,0 +1,240 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+part of dart._internal;
+
+/// Builds a list of bytes, allowing bytes and lists of bytes to be added at the
+/// end.
+///
+/// Used to efficiently collect bytes and lists of bytes.
+abstract class BytesBuilder {
+  /// Construct a new empty [BytesBuilder].
+  ///
+  /// If [copy] is true (the default), the created builder is a *copying*
+  /// builder. A copying builder maintains its own internal buffer and copies
+  /// the bytes added to it eagerly.
+  ///
+  /// If [copy] set to false, the created builder assumes that lists added
+  /// to it will not change.
+  /// Any [Uint8List] added using [add] is kept until
+  /// [toBytes] or [takeBytes] is called,
+  /// and only then are their contents copied.
+  /// A non-[Uint8List] may be copied eagerly.
+  /// If only a single [Uint8List] is added to the builder,
+  /// that list is returned by [toBytes] or [takeBytes] directly, without any copying.
+  /// A list added to a non-copying builder *should not* change its content
+  /// after being added, and it *must not* change its length after being added.
+  /// (Normal [Uint8List]s are fixed length lists, but growing lists implementing
+  /// [Uint8List] exist.)
+  factory BytesBuilder({bool copy = true}) =>
+      copy ? _CopyingBytesBuilder() : _BytesBuilder();
+
+  /// Appends [bytes] to the current contents of this builder.
+  ///
+  /// Each value of [bytes] will be truncated
+  /// to an 8-bit value in the range 0 .. 255.
+  void add(List<int> bytes);
+
+  /// Appends [byte] to the current contents of this builder.
+  ///
+  /// The [byte] will be truncated to an 8-bit value in the range 0 .. 255.
+  void addByte(int byte);
+
+  /// Returns the bytes currently contained in this builder and clears it.
+  ///
+  /// The returned list may be a view of a larger buffer.
+  Uint8List takeBytes();
+
+  /// Returns a copy of the current byte contents of this builder.
+  ///
+  /// Leaves the contents of this builder intact.
+  Uint8List toBytes();
+
+  /// The number of bytes in this builder.
+  int get length;
+
+  /// Whether the buffer is empty.
+  bool get isEmpty;
+
+  /// Whether the buffer is non-empty.
+  bool get isNotEmpty;
+
+  /// Clears the contents of this builder.
+  ///
+  /// The current contents are discarded and this builder becomes empty.
+  void clear();
+}
+
+/// A [BytesBuilder] which appends bytes to a growing internal buffer.
+class _CopyingBytesBuilder implements BytesBuilder {
+  /// Initial size of internal buffer.
+  static const int _initSize = 1024;
+
+  /// Reusable empty [Uint8List].
+  ///
+  /// Safe for reuse because a fixed-length empty list is immutable.
+  static final _emptyList = Uint8List(0);
+
+  /// Current count of bytes written to buffer.
+  int _length = 0;
+
+  /// Internal buffer accumulating bytes.
+  ///
+  /// Will grow as necessary
+  Uint8List _buffer;
+
+  _CopyingBytesBuilder() : _buffer = _emptyList;
+
+  void add(List<int> bytes) {
+    int byteCount = bytes.length;
+    if (byteCount == 0) return;
+    int required = _length + byteCount;
+    if (_buffer.length < required) {
+      _grow(required);
+    }
+    assert(_buffer.length >= required);
+    if (bytes is Uint8List) {
+      _buffer.setRange(_length, required, bytes);
+    } else {
+      for (int i = 0; i < byteCount; i++) {
+        _buffer[_length + i] = bytes[i];
+      }
+    }
+    _length = required;
+  }
+
+  void addByte(int byte) {
+    if (_buffer.length == _length) {
+      // The grow algorithm always at least doubles.
+      // If we added one to _length it would quadruple unnecessarily.
+      _grow(_length);
+    }
+    assert(_buffer.length > _length);
+    _buffer[_length] = byte;
+    _length++;
+  }
+
+  void _grow(int required) {
+    // We will create a list in the range of 2-4 times larger than
+    // required.
+    int newSize = required * 2;
+    if (newSize < _initSize) {
+      newSize = _initSize;
+    } else {
+      newSize = _pow2roundup(newSize);
+    }
+    var newBuffer = Uint8List(newSize);
+    newBuffer.setRange(0, _buffer.length, _buffer);
+    _buffer = newBuffer;
+  }
+
+  Uint8List takeBytes() {
+    if (_length == 0) return _emptyList;
+    var buffer = Uint8List.view(_buffer.buffer, _buffer.offsetInBytes, _length);
+    _clear();
+    return buffer;
+  }
+
+  Uint8List toBytes() {
+    if (_length == 0) return _emptyList;
+    return Uint8List.fromList(
+        Uint8List.view(_buffer.buffer, _buffer.offsetInBytes, _length));
+  }
+
+  int get length => _length;
+
+  bool get isEmpty => _length == 0;
+
+  bool get isNotEmpty => _length != 0;
+
+  void clear() {
+    _clear();
+  }
+
+  void _clear() {
+    _length = 0;
+    _buffer = _emptyList;
+  }
+
+  /// Rounds numbers <= 2^32 up to the nearest power of 2.
+  static int _pow2roundup(int x) {
+    assert(x > 0);
+    --x;
+    x |= x >> 1;
+    x |= x >> 2;
+    x |= x >> 4;
+    x |= x >> 8;
+    x |= x >> 16;
+    return x + 1;
+  }
+}
+
+/// A non-copying [BytesBuilder].
+///
+/// Accumulates lists of integers and lazily builds
+/// a collected list with all the bytes when requested.
+class _BytesBuilder implements BytesBuilder {
+  int _length = 0;
+  final List<Uint8List> _chunks = [];
+
+  void add(List<int> bytes) {
+    Uint8List typedBytes;
+    if (bytes is Uint8List) {
+      typedBytes = bytes;
+    } else {
+      typedBytes = Uint8List.fromList(bytes);
+    }
+    _chunks.add(typedBytes);
+    _length += typedBytes.length;
+  }
+
+  void addByte(int byte) {
+    // TODO(lrn): Optimize repeated `addByte` calls.
+    _chunks.add(Uint8List(1)..[0] = byte);
+    _length++;
+  }
+
+  Uint8List takeBytes() {
+    if (_length == 0) return _CopyingBytesBuilder._emptyList;
+    if (_chunks.length == 1) {
+      var buffer = _chunks[0];
+      _clear();
+      return buffer;
+    }
+    var buffer = Uint8List(_length);
+    int offset = 0;
+    for (var chunk in _chunks) {
+      buffer.setRange(offset, offset + chunk.length, chunk);
+      offset += chunk.length;
+    }
+    _clear();
+    return buffer;
+  }
+
+  Uint8List toBytes() {
+    if (_length == 0) return _CopyingBytesBuilder._emptyList;
+    var buffer = Uint8List(_length);
+    int offset = 0;
+    for (var chunk in _chunks) {
+      buffer.setRange(offset, offset + chunk.length, chunk);
+      offset += chunk.length;
+    }
+    return buffer;
+  }
+
+  int get length => _length;
+
+  bool get isEmpty => _length == 0;
+
+  bool get isNotEmpty => _length != 0;
+
+  void clear() {
+    _clear();
+  }
+
+  void _clear() {
+    _length = 0;
+    _chunks.clear();
+  }
+}
diff --git a/sdk/lib/internal/internal.dart b/sdk/lib/internal/internal.dart
index dad3b05cc14..3070b3080db 100644
--- a/sdk/lib/internal/internal.dart
+++ b/sdk/lib/internal/internal.dart
@@ -21,6 +21,7 @@ import 'dart:math' show Random;
 import 'dart:typed_data' show Uint8List;
 
 part 'async_cast.dart';
+part 'bytes_builder.dart';
 part 'cast.dart';
 part 'errors.dart';
 part 'iterable.dart';
diff --git a/sdk/lib/internal/internal_sources.gni b/sdk/lib/internal/internal_sources.gni
index 8510ab2d881..c35e678ed51 100644
--- a/sdk/lib/internal/internal_sources.gni
+++ b/sdk/lib/internal/internal_sources.gni
@@ -8,6 +8,7 @@ internal_sdk_sources = [
 
   # The above file needs to be first as it lists the parts below.
   "async_cast.dart",
+  "bytes_builder.dart",
   "cast.dart",
   "errors.dart",
   "iterable.dart",
diff --git a/sdk/lib/io/bytes_builder.dart b/sdk/lib/io/bytes_builder.dart
deleted file mode 100644
index 6f13693a031..00000000000
--- a/sdk/lib/io/bytes_builder.dart
+++ /dev/null
@@ -1,234 +0,0 @@
-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-part of dart.io;
-
-/**
- * Builds a list of bytes, allowing bytes and lists of bytes to be added at the
- * end.
- *
- * Used to efficiently collect bytes and lists of bytes.
- */
-abstract class BytesBuilder {
-  /**
-   * Construct a new empty [BytesBuilder].
-   *
-   * If [copy] is true, the data is always copied when added to the list. If
-   * it [copy] is false, the data is only copied if needed. That means that if
-   * the lists are changed after added to the [BytesBuilder], it may effect the
-   * output. Default is `true`.
-   */
-  factory BytesBuilder({bool copy: true}) {
-    if (copy) {
-      return new _CopyingBytesBuilder();
-    } else {
-      return new _BytesBuilder();
-    }
-  }
-
-  /**
-   * Appends [bytes] to the current contents of the builder.
-   *
-   * Each value of [bytes] will be bit-representation truncated to the range
-   * 0 .. 255.
-   */
-  void add(List<int> bytes);
-
-  /**
-   * Append [byte] to the current contents of the builder.
-   *
-   * The [byte] will be bit-representation truncated to the range 0 .. 255.
-   */
-  void addByte(int byte);
-
-  /**
-   * Returns the contents of `this` and clears `this`.
-   *
-   * The list returned is a view of the internal buffer, limited to the
-   * [length].
-   */
-  Uint8List takeBytes();
-
-  /**
-   * Returns a copy of the current contents of the builder.
-   *
-   * Leaves the contents of the builder intact.
-   */
-  Uint8List toBytes();
-
-  /**
-   * The number of bytes in the builder.
-   */
-  int get length;
-
-  /**
-   * Returns `true` if the buffer is empty.
-   */
-  bool get isEmpty;
-
-  /**
-   * Returns `true` if the buffer is not empty.
-   */
-  bool get isNotEmpty;
-
-  /**
-   * Clear the contents of the builder.
-   */
-  void clear();
-}
-
-class _CopyingBytesBuilder implements BytesBuilder {
-  // Start with 1024 bytes.
-  static const int _initSize = 1024;
-
-  // Safe for reuse because a fixed-length empty list is immutable.
-  static final _emptyList = new Uint8List(0);
-
-  int _length = 0;
-  Uint8List _buffer;
-
-  _CopyingBytesBuilder([int initialCapacity = 0])
-      : _buffer = (initialCapacity <= 0)
-            ? _emptyList
-            : new Uint8List(_pow2roundup(initialCapacity));
-
-  void add(List<int> bytes) {
-    int bytesLength = bytes.length;
-    if (bytesLength == 0) return;
-    int required = _length + bytesLength;
-    if (_buffer.length < required) {
-      _grow(required);
-    }
-    assert(_buffer.length >= required);
-    if (bytes is Uint8List) {
-      _buffer.setRange(_length, required, bytes);
-    } else {
-      for (int i = 0; i < bytesLength; i++) {
-        _buffer[_length + i] = bytes[i];
-      }
-    }
-    _length = required;
-  }
-
-  void addByte(int byte) {
-    if (_buffer.length == _length) {
-      // The grow algorithm always at least doubles.
-      // If we added one to _length it would quadruple unnecessarily.
-      _grow(_length);
-    }
-    assert(_buffer.length > _length);
-    _buffer[_length] = byte;
-    _length++;
-  }
-
-  void _grow(int required) {
-    // We will create a list in the range of 2-4 times larger than
-    // required.
-    int newSize = required * 2;
-    if (newSize < _initSize) {
-      newSize = _initSize;
-    } else {
-      newSize = _pow2roundup(newSize);
-    }
-    var newBuffer = new Uint8List(newSize);
-    newBuffer.setRange(0, _buffer.length, _buffer);
-    _buffer = newBuffer;
-  }
-
-  Uint8List takeBytes() {
-    if (_length == 0) return _emptyList;
-    var buffer =
-        new Uint8List.view(_buffer.buffer, _buffer.offsetInBytes, _length);
-    clear();
-    return buffer;
-  }
-
-  Uint8List toBytes() {
-    if (_length == 0) return _emptyList;
-    return new Uint8List.fromList(
-        new Uint8List.view(_buffer.buffer, _buffer.offsetInBytes, _length));
-  }
-
-  int get length => _length;
-
-  bool get isEmpty => _length == 0;
-
-  bool get isNotEmpty => _length != 0;
-
-  void clear() {
-    _length = 0;
-    _buffer = _emptyList;
-  }
-
-  static int _pow2roundup(int x) {
-    assert(x > 0);
-    --x;
-    x |= x >> 1;
-    x |= x >> 2;
-    x |= x >> 4;
-    x |= x >> 8;
-    x |= x >> 16;
-    return x + 1;
-  }
-}
-
-class _BytesBuilder implements BytesBuilder {
-  int _length = 0;
-  final List<Uint8List> _chunks = [];
-
-  void add(List<int> bytes) {
-    Uint8List typedBytes;
-    if (bytes is Uint8List) {
-      typedBytes = bytes;
-    } else {
-      typedBytes = new Uint8List.fromList(bytes);
-    }
-    _chunks.add(typedBytes);
-    _length += typedBytes.length;
-  }
-
-  void addByte(int byte) {
-    _chunks.add(new Uint8List(1)..[0] = byte);
-    _length++;
-  }
-
-  Uint8List takeBytes() {
-    if (_length == 0) return _CopyingBytesBuilder._emptyList;
-    if (_chunks.length == 1) {
-      var buffer = _chunks[0];
-      clear();
-      return buffer;
-    }
-    var buffer = new Uint8List(_length);
-    int offset = 0;
-    for (var chunk in _chunks) {
-      buffer.setRange(offset, offset + chunk.length, chunk);
-      offset += chunk.length;
-    }
-    clear();
-    return buffer;
-  }
-
-  Uint8List toBytes() {
-    if (_length == 0) return _CopyingBytesBuilder._emptyList;
-    var buffer = new Uint8List(_length);
-    int offset = 0;
-    for (var chunk in _chunks) {
-      buffer.setRange(offset, offset + chunk.length, chunk);
-      offset += chunk.length;
-    }
-    return buffer;
-  }
-
-  int get length => _length;
-
-  bool get isEmpty => _length == 0;
-
-  bool get isNotEmpty => _length != 0;
-
-  void clear() {
-    _length = 0;
-    _chunks.clear();
-  }
-}
diff --git a/sdk/lib/io/io.dart b/sdk/lib/io/io.dart
index 7dcabd83d91..c667cfe5852 100644
--- a/sdk/lib/io/io.dart
+++ b/sdk/lib/io/io.dart
@@ -197,9 +197,10 @@ import 'dart:math';
 import 'dart:typed_data';
 
 export 'dart:_http';
+@Deprecated("Import BytesBuilder from dart:typed_data instead")
+export 'dart:_internal' show BytesBuilder;
 export 'dart:_internal' show HttpStatus;
 
-part 'bytes_builder.dart';
 part 'common.dart';
 part 'data_transformer.dart';
 part 'directory.dart';
diff --git a/sdk/lib/io/io_sources.gni b/sdk/lib/io/io_sources.gni
index 59b2ca957d0..7410a13530e 100644
--- a/sdk/lib/io/io_sources.gni
+++ b/sdk/lib/io/io_sources.gni
@@ -6,7 +6,6 @@ io_sdk_sources = [
   "io.dart",
 
   # The above file needs to be first if additional parts are added to the lib.
-  "bytes_builder.dart",
   "common.dart",
   "data_transformer.dart",
   "directory.dart",
diff --git a/sdk/lib/typed_data/typed_data.dart b/sdk/lib/typed_data/typed_data.dart
index 8852ab89545..eeafdc62b08 100644
--- a/sdk/lib/typed_data/typed_data.dart
+++ b/sdk/lib/typed_data/typed_data.dart
@@ -14,6 +14,8 @@ library dart.typed_data;
 
 import "dart:_internal" show Since, UnmodifiableListBase;
 
+export "dart:_internal" show BytesBuilder;
+
 part "unmodifiable_typed_data.dart";
 
 /**
diff --git a/tests/standalone/io/bytes_builder_test.dart b/tests/lib/typed_data/bytes_builder_test.dart
similarity index 98%
rename from tests/standalone/io/bytes_builder_test.dart
rename to tests/lib/typed_data/bytes_builder_test.dart
index 5b6a6b9158e..5c1dd693de0 100644
--- a/tests/standalone/io/bytes_builder_test.dart
+++ b/tests/lib/typed_data/bytes_builder_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import "dart:io";
 import "dart:typed_data";
 import "package:expect/expect.dart";
 
diff --git a/tests/standalone_2/io/bytes_builder_test.dart b/tests/lib_2/typed_data/bytes_builder_test.dart
similarity index 98%
rename from tests/standalone_2/io/bytes_builder_test.dart
rename to tests/lib_2/typed_data/bytes_builder_test.dart
index 5b6a6b9158e..5c1dd693de0 100644
--- a/tests/standalone_2/io/bytes_builder_test.dart
+++ b/tests/lib_2/typed_data/bytes_builder_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import "dart:io";
 import "dart:typed_data";
 import "package:expect/expect.dart";