diff --git a/.travis.yml b/.travis.yml
index 88875276..67936413 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,7 +4,6 @@ dart:
   - dev
   - stable
   - 1.22.1
-  - 1.21.1
 cache:
   directories:
     - $HOME/.pub-cache
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 41c10e08..3ecc06d2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.5.6
+
+* Support for package:build 0.9.0
+
 ## 0.5.5
 
 * Support package:build 0.8.x
diff --git a/lib/src/builder.dart b/lib/src/builder.dart
index 2705a88c..e052bde7 100644
--- a/lib/src/builder.dart
+++ b/lib/src/builder.dart
@@ -35,10 +35,9 @@ class GeneratorBuilder extends Builder {
   }
 
   @override
-  List<AssetId> declareOutputs(AssetId input) {
-    if (input.extension != '.dart') return const [];
-    return [_generatedFile(input)];
-  }
+  Map<String, List<String>> get buildExtensions => {
+        '.dart': [generatedExtension]
+      };
 
   AssetId _generatedFile(AssetId input) =>
       input.changeExtension(generatedExtension);
diff --git a/pubspec.yaml b/pubspec.yaml
index 27568f18..a8e072fd 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: source_gen
-version: 0.5.5
+version: 0.5.6
 author: Dart Team <misc@dartlang.org>
 description: Automatic sourcecode generation for Dart
 homepage: https://github.com/dart-lang/source_gen
@@ -7,12 +7,12 @@ environment:
   sdk: '>=1.21.1 <2.0.0'
 dependencies:
   analyzer: ^0.29.2
-  build: '>=0.7.1 <0.9.0'
+  build: ^0.9.0
   dart_style: '>=0.1.7 <2.0.0'
   path: ^1.3.2
 dev_dependencies:
-  build_runner: ^0.3.1+1
-  build_test: ^0.5.1
+  build_runner: ^0.3.2
+  build_test: ^0.6.0
   cli_util: ^0.0.1
   collection: ^1.1.2
   mockito: '>=0.11.0 <3.0.0'