diff --git a/lib/printer.dart b/lib/printer.dart
index 95539d2..0898017 100644
--- a/lib/printer.dart
+++ b/lib/printer.dart
@@ -5,7 +5,6 @@
 /// Contains a code printer that generates code by recording the source maps.
 library source_maps.printer;
 
-import 'dart:utf' show stringToCodepoints;
 import 'builder.dart';
 import 'span.dart';
 
@@ -38,7 +37,7 @@
   /// line in the target file (printed here) corresponds to a new line in the
   /// source file.
   void add(String str, {projectMarks: false}) {
-    var chars = stringToCodepoints(str);
+    var chars = str.runes.toList();
     var length = chars.length;
     for (int i = 0; i < length; i++) {
       var c = chars[i];
diff --git a/lib/span.dart b/lib/span.dart
index e5057fc..17ccd27 100644
--- a/lib/span.dart
+++ b/lib/span.dart
@@ -5,7 +5,6 @@
 /// Dart classes representing the souce spans and source files.
 library source_maps.span;
 
-import 'dart:utf' show stringToCodepoints;
 import 'dart:math' show min, max;
 
 import 'src/utils.dart';
@@ -201,7 +200,7 @@
 
   SourceFile.text(this.url, String text)
       : _lineStarts = <int>[0],
-        _decodedChars = stringToCodepoints(text) {
+        _decodedChars = text.runes.toList() {
     for (int i = 0; i < _decodedChars.length; i++) {
       var c = _decodedChars[i];
       if (c == _CR) {