diff --git a/sdk/lib/_internal/compiler/implementation/dart2js.dart b/sdk/lib/_internal/compiler/implementation/dart2js.dart
index f51abf55c92..bc9c6becb27 100644
--- a/sdk/lib/_internal/compiler/implementation/dart2js.dart
+++ b/sdk/lib/_internal/compiler/implementation/dart2js.dart
@@ -376,7 +376,7 @@ Future compile(List<String> argv) {
     }
 
     RandomAccessFile output =
-        new File(uriPathToNative(uri.path)).openSync(mode: FileMode.WRITE);
+        new File(uri.toFilePath()).openSync(mode: FileMode.WRITE);
     int charactersWritten = 0;
 
     writeStringSync(String data) {
@@ -445,7 +445,7 @@ void writeString(Uri uri, String text) {
   if (uri.scheme != 'file') {
     fail('Error: Unhandled scheme ${uri.scheme}.');
   }
-  var file = new File(uriPathToNative(uri.path)).openSync(mode: FileMode.WRITE);
+  var file = new File(uri.toFilePath()).openSync(mode: FileMode.WRITE);
   file.writeStringSync(text);
   file.closeSync();
 }
diff --git a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
index 78ad54785fa..775841d0362 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
@@ -971,6 +971,9 @@ class LibraryElementX extends ElementX implements LibraryElement {
    * Returns the library name (as defined by the library tag) or for script
    * (which have no library tag) the script file name. The latter case is used
    * to private 'library name' for scripts to use for instance in dartdoc.
+   *
+   * Note: the returned filename will still be escaped ("a%20b.dart" instead of
+   * "a b.dart").
    */
   String getLibraryOrScriptName() {
     if (libraryTag != null) {
diff --git a/sdk/lib/_internal/compiler/implementation/source_file_provider.dart b/sdk/lib/_internal/compiler/implementation/source_file_provider.dart
index 4640ff50517..ab11a776404 100644
--- a/sdk/lib/_internal/compiler/implementation/source_file_provider.dart
+++ b/sdk/lib/_internal/compiler/implementation/source_file_provider.dart
@@ -42,7 +42,7 @@ abstract class SourceFileProvider {
     }
     List<int> source;
     try {
-      source = readAll(uriPathToNative(resourceUri.path));
+      source = readAll(resourceUri.toFilePath());
     } on FileSystemException catch (ex) {
       return new Future.error(
           "Error reading '${relativize(cwd, resourceUri, isWindows)}' "
diff --git a/tests/compiler/dart2js/async_compiler_input_provider_test.dart b/tests/compiler/dart2js/async_compiler_input_provider_test.dart
index 6a4502218a2..7f370c31267 100644
--- a/tests/compiler/dart2js/async_compiler_input_provider_test.dart
+++ b/tests/compiler/dart2js/async_compiler_input_provider_test.dart
@@ -31,7 +31,7 @@ Future<String> provideInput(Uri uri) {
   var source = SOURCES[uri.path];
   if (source == null) {
     // Not one of our source files, so assume it's a built-in.
-    source = new File(uriPathToNative(uri.path)).readAsStringSync();
+    source = new File(uri.toFilePath()).readAsStringSync();
   }
 
   // Deliver the input asynchronously.
diff --git a/tests/compiler/dart2js/path with spaces/file with spaces.dart b/tests/compiler/dart2js/path with spaces/file with spaces.dart
new file mode 100644
index 00000000000..b0cc20402f8
--- /dev/null
+++ b/tests/compiler/dart2js/path with spaces/file with spaces.dart	
@@ -0,0 +1,9 @@
+// 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 'library space/lib with spaces.dart';
+
+main() {
+  if (foo() != 499) throw "bad value";
+}
diff --git a/tests/compiler/dart2js/path with spaces/library space/lib with spaces.dart b/tests/compiler/dart2js/path with spaces/library space/lib with spaces.dart
new file mode 100644
index 00000000000..16da6e3295b
--- /dev/null
+++ b/tests/compiler/dart2js/path with spaces/library space/lib with spaces.dart	
@@ -0,0 +1,9 @@
+// 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.
+
+library spaces;
+
+part "part space/part space.dart";
+
+foo() => bar();
diff --git a/tests/compiler/dart2js/path with spaces/library space/part space/part space.dart b/tests/compiler/dart2js/path with spaces/library space/part space/part space.dart
new file mode 100644
index 00000000000..58aff0fb6e8
--- /dev/null
+++ b/tests/compiler/dart2js/path with spaces/library space/part space/part space.dart	
@@ -0,0 +1,7 @@
+// 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.
+
+part of spaces;
+
+bar() => 499;
diff --git a/tests/compiler/dart2js/space_test.dart b/tests/compiler/dart2js/space_test.dart
new file mode 100644
index 00000000000..6eeafcd94a2
--- /dev/null
+++ b/tests/compiler/dart2js/space_test.dart
@@ -0,0 +1,18 @@
+// 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 'dart:io';
+import '../../../sdk/lib/_internal/compiler/implementation/dart2js.dart'
+  as dart2js;
+
+main() {
+  Uri currentDirectory = Uri.base;
+  Uri script = currentDirectory.resolveUri(Platform.script);
+  Uri libraryRoot = script.resolve('../../../sdk/');
+  Directory.current = script.resolve("path with spaces").toFilePath();
+
+  return dart2js.main(["--library-root=${libraryRoot.toFilePath()}",
+                       "--analyze-only",
+                       "file with spaces.dart"]);
+}