diff --git a/lib/src/short/fast_hash.dart b/lib/src/fast_hash.dart
similarity index 100%
rename from lib/src/short/fast_hash.dart
rename to lib/src/fast_hash.dart
diff --git a/lib/src/piece/piece.dart b/lib/src/piece/piece.dart
index 348bb43d..e44cac13 100644
--- a/lib/src/piece/piece.dart
+++ b/lib/src/piece/piece.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import '../back_end/code_writer.dart';
+import '../fast_hash.dart';
 import '../profile.dart';
 
 typedef Constrain = void Function(Piece other, State constrainedState);
@@ -14,7 +15,7 @@ typedef Constrain = void Function(Piece other, State constrainedState);
 /// roughly follows the AST but includes comments and is optimized for
 /// formatting and line splitting. The final output is then determined by
 /// deciding which pieces split and how.
-abstract base class Piece {
+abstract base class Piece with FastHash {
   /// The ordered list of all possible ways this piece could split.
   ///
   /// Piece subclasses should override this if they support being split in
@@ -190,7 +191,7 @@ abstract base class Piece {
   String get debugName => runtimeType.toString().replaceAll('Piece', '');
 
   @override
-  String toString() => '$debugName${_pinnedState ?? ''}';
+  String toString() => '$debugName$id${_pinnedState ?? ''}';
 }
 
 /// A state that a piece can be in.
diff --git a/lib/src/short/chunk.dart b/lib/src/short/chunk.dart
index c37ed110..9af7b879 100644
--- a/lib/src/short/chunk.dart
+++ b/lib/src/short/chunk.dart
@@ -1,8 +1,8 @@
 // Copyright (c) 2014, 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.
+import '../fast_hash.dart';
 import '../profile.dart';
-import 'fast_hash.dart';
 import 'marking_scheme.dart';
 import 'nesting_level.dart';
 import 'rule/rule.dart';
diff --git a/lib/src/short/nesting_level.dart b/lib/src/short/nesting_level.dart
index 0040233f..6260b533 100644
--- a/lib/src/short/nesting_level.dart
+++ b/lib/src/short/nesting_level.dart
@@ -2,7 +2,7 @@
 // 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 'fast_hash.dart';
+import '../fast_hash.dart';
 import 'marking_scheme.dart';
 
 /// A single level of expression nesting.
diff --git a/lib/src/short/rule/rule.dart b/lib/src/short/rule/rule.dart
index 393d48d7..62f48228 100644
--- a/lib/src/short/rule/rule.dart
+++ b/lib/src/short/rule/rule.dart
@@ -3,9 +3,9 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import '../../constants.dart';
+import '../../fast_hash.dart';
 import '../../profile.dart';
 import '../chunk.dart';
-import '../fast_hash.dart';
 
 /// A constraint that determines the different ways a related set of chunks may
 /// be split.