diff --git a/pkg/dev_compiler/bin/dartdevc.dart b/pkg/dev_compiler/bin/dartdevc.dart
index db2f7b8..276320d 100755
--- a/pkg/dev_compiler/bin/dartdevc.dart
+++ b/pkg/dev_compiler/bin/dartdevc.dart
@@ -52,7 +52,20 @@
     var args = _startupArgs.merge(request.arguments);
     var output = StringBuffer();
     var context = args.reuseResult ? lastResult : null;
-    lastResult = await runZoned(() => compile(args, previousResult: context),
+
+    /// Build a map of uris to digests.
+    final inputDigests = <Uri, List<int>>{};
+    for (var input in request.inputs) {
+      var uri = Uri.parse(input.path);
+      if (uri.scheme.isEmpty) {
+        uri = Uri.parse('file://${input.path}');
+      }
+      inputDigests[uri] = input.digest;
+    }
+
+    lastResult = await runZoned(
+        () =>
+            compile(args, previousResult: context, inputDigests: inputDigests),
         zoneSpecification:
             ZoneSpecification(print: (self, parent, zone, message) {
       output.writeln(message.toString());
diff --git a/pkg/dev_compiler/lib/src/compiler/shared_command.dart b/pkg/dev_compiler/lib/src/compiler/shared_command.dart
index 0388456..c30e7a9 100644
--- a/pkg/dev_compiler/lib/src/compiler/shared_command.dart
+++ b/pkg/dev_compiler/lib/src/compiler/shared_command.dart
@@ -400,7 +400,7 @@
 /// The result may also contain a [previousResult], which can be passed back in
 /// for batch/worker executions to attempt to existing state.
 Future<CompilerResult> compile(ParsedArguments args,
-    {CompilerResult previousResult}) {
+    {CompilerResult previousResult, Map<Uri, List<int>> inputDigests}) {
   if (previousResult != null && !args.isBatchOrWorker) {
     throw ArgumentError(
         'previousResult requires --batch or --bazel_worker mode/');
@@ -408,7 +408,8 @@
   if (args.isKernel) {
     return kernel_compiler.compile(args.rest,
         compilerState: previousResult?.kernelState,
-        useIncrementalCompiler: args.useIncrementalCompiler);
+        useIncrementalCompiler: args.useIncrementalCompiler,
+        inputDigests: inputDigests);
   } else {
     var result = analyzer_compiler.compile(args.rest,
         compilerState: previousResult?.analyzerState);
diff --git a/pkg/dev_compiler/lib/src/kernel/command.dart b/pkg/dev_compiler/lib/src/kernel/command.dart
index ca85c12..ecd4d84 100644
--- a/pkg/dev_compiler/lib/src/kernel/command.dart
+++ b/pkg/dev_compiler/lib/src/kernel/command.dart
@@ -37,11 +37,13 @@
 /// Returns `true` if the program compiled without any fatal errors.
 Future<CompilerResult> compile(List<String> args,
     {fe.InitializedCompilerState compilerState,
-    bool useIncrementalCompiler = false}) async {
+    bool useIncrementalCompiler = false,
+    Map<Uri, List<int>> inputDigests}) async {
   try {
     return await _compile(args,
         compilerState: compilerState,
-        useIncrementalCompiler: useIncrementalCompiler);
+        useIncrementalCompiler: useIncrementalCompiler,
+        inputDigests: inputDigests);
   } catch (error, stackTrace) {
     print('''
 We're sorry, you've found a bug in our compiler.
@@ -68,7 +70,8 @@
 
 Future<CompilerResult> _compile(List<String> args,
     {fe.InitializedCompilerState compilerState,
-    bool useIncrementalCompiler = false}) async {
+    bool useIncrementalCompiler = false,
+    Map<Uri, List<int>> inputDigests}) async {
   // TODO(jmesserly): refactor options to share code with dartdevc CLI.
   var argParser = ArgParser(allowTrailingOptions: true)
     ..addFlag('help',
@@ -253,6 +256,7 @@
         sourcePathToUri(packageFile),
         sourcePathToUri(librarySpecPath),
         summaryModules.keys.toList(),
+        inputDigests,
         DevCompilerTarget(
             TargetFlags(trackWidgetCreation: trackWidgetCreation)),
         fileSystem: fileSystem,
diff --git a/pkg/front_end/lib/src/api_unstable/ddc.dart b/pkg/front_end/lib/src/api_unstable/ddc.dart
index 4c2076b..a344601 100644
--- a/pkg/front_end/lib/src/api_unstable/ddc.dart
+++ b/pkg/front_end/lib/src/api_unstable/ddc.dart
@@ -131,6 +131,7 @@
     Uri packagesFile,
     Uri librariesSpecificationUri,
     List<Uri> inputSummaries,
+    Map<Uri, List<int>> workerInputDigests,
     Target target,
     {FileSystem fileSystem,
     Map<ExperimentalFlag, bool> experiments}) async {
@@ -143,12 +144,18 @@
 
   Map<Uri, WorkerInputComponent> workerInputCache =
       oldState?.workerInputCache ?? new Map<Uri, WorkerInputComponent>();
+  var sdkDigest = workerInputDigests[sdkSummary];
+  if (sdkDigest == null) {
+    throw new StateError("Expected to get sdk digest at $cachedSdkInput");
+  }
+
   cachedSdkInput = workerInputCache[sdkSummary];
 
   if (oldState == null ||
       oldState.incrementalCompiler == null ||
       oldState.options.compileSdk != compileSdk ||
-      cachedSdkInput == null) {
+      cachedSdkInput == null ||
+      !digestsEqual(cachedSdkInput.digest, sdkDigest)) {
     // No previous state.
     options = new CompilerOptions()
       ..compileSdk = compileSdk
@@ -166,8 +173,8 @@
 
     processedOpts = new ProcessedOptions(options: options);
 
-    cachedSdkInput = new WorkerInputComponent(null /* not compared anyway */,
-        await processedOpts.loadSdkSummary(null));
+    cachedSdkInput = new WorkerInputComponent(
+        sdkDigest, await processedOpts.loadSdkSummary(null));
     workerInputCache[sdkSummary] = cachedSdkInput;
     incrementalCompiler = new IncrementalCompiler.fromComponent(
         new CompilerContext(processedOpts), cachedSdkInput.component);
@@ -207,10 +214,13 @@
   for (int i = 0; i < inputSummaries.length; i++) {
     Uri inputSummary = inputSummaries[i];
     WorkerInputComponent cachedInput = workerInputCache[inputSummary];
+    var digest = workerInputDigests[inputSummary];
+    if (digest == null) {
+      throw new StateError("Expected to get digest for $inputSummary");
+    }
     if (cachedInput == null ||
         cachedInput.component.root != nameRoot ||
-        !digestsEqual(await fileSystem.entityForUri(inputSummary).readAsBytes(),
-            cachedInput.digest)) {
+        !digestsEqual(digest, cachedInput.digest)) {
       loadFromDillIndexes.add(i);
     } else {
       // Need to reset cached components so they are usable again.
@@ -226,11 +236,15 @@
   for (int i = 0; i < loadFromDillIndexes.length; i++) {
     int index = loadFromDillIndexes[i];
     Uri summary = inputSummaries[index];
-    List<int> data = await fileSystem.entityForUri(summary).readAsBytes();
+    List<int> digest = workerInputDigests[summary];
+    if (digest == null) {
+      throw new StateError("Expected to get digest for $summary");
+    }
+    var bytes = await fileSystem.entityForUri(summary).readAsBytes();
     WorkerInputComponent cachedInput = WorkerInputComponent(
-        data,
+        digest,
         await compilerState.processedOpts
-            .loadComponent(data, nameRoot, alwaysCreateNewNamedNodes: true));
+            .loadComponent(bytes, nameRoot, alwaysCreateNewNamedNodes: true));
     workerInputCache[summary] = cachedInput;
     doneInputSummaries[index] = cachedInput.component;
   }