diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3320989..dbf745c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,9 @@
 This file contains highlights of what changes on each version of the html
 package.
 
+## 0.13.1
+ * Update Set.difference to take a Set<Object>.
+
 ## 0.13.0
 
  * **BREAKING** Fix all [strong mode][] errors and warnings.
diff --git a/lib/src/css_class_set.dart b/lib/src/css_class_set.dart
index c7927b8..ddc1612 100644
--- a/lib/src/css_class_set.dart
+++ b/lib/src/css_class_set.dart
@@ -271,7 +271,7 @@
 
   Set<String> union(Set<String> other) => readClasses().union(other);
 
-  Set<String> difference(Set<String> other) => readClasses().difference(other);
+  Set<String> difference(Set<Object> other) => readClasses().difference(other);
 
   String get first => readClasses().first;
   String get last => readClasses().last;
diff --git a/pubspec.yaml b/pubspec.yaml
index 4a595c1..cceb1e4 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,10 +1,10 @@
 name: html
-version: 0.13.0
+version: 0.13.1
 author: Dart Team <misc@dartlang.org>
 description: A library for working with HTML documents. Previously known as html5lib.
 homepage: https://github.com/dart-lang/html
 environment:
-  sdk: '>=1.2.0 <2.0.0'
+  sdk: '>=1.21.0-dev.2.0 <2.0.0'
 dependencies:
   csslib: '>=0.13.2 <0.14.0'
   source_span: '>=1.0.0 <2.0.0'