diff --git a/pkg/front_end/lib/src/api_prototype/standard_file_system.dart b/pkg/front_end/lib/src/api_prototype/standard_file_system.dart
index 5be815e..bdd78ad 100644
--- a/pkg/front_end/lib/src/api_prototype/standard_file_system.dart
+++ b/pkg/front_end/lib/src/api_prototype/standard_file_system.dart
@@ -63,7 +63,7 @@
   Future<List<int>> readAsBytes() async {
     try {
       CompilerContext.recordDependency(uri);
-      return await new io.File.fromUri(uri).readAsBytes();
+      return new io.File.fromUri(uri).readAsBytesSync();
     } on io.FileSystemException catch (exception) {
       throw _toFileSystemException(exception);
     }