diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0ec7d68ad1d..8571676399f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,7 +2,8 @@
 
 * `dart:core`
   * `Uri` added `removeFragment` method.
-
+  * `String.allMatches` (implementing `Pattern.allMatches`) is now lazy,
+    as all `allMatches` implementations are intended to be.
 * `dart:io`
   * `HttpClient` no longer sends URI fragments in the requeust. This is not
     allowed by the HTTP protocol.
diff --git a/runtime/lib/string_patch.dart b/runtime/lib/string_patch.dart
index 21a5ab0090f..eb1a2a29553 100644
--- a/runtime/lib/string_patch.dart
+++ b/runtime/lib/string_patch.dart
@@ -312,7 +312,7 @@ class _StringBase {
 
   int indexOf(Pattern pattern, [int start = 0]) {
     if ((start < 0) || (start > this.length)) {
-      throw new RangeError.range(start, 0, this.length);
+      throw new RangeError.range(start, 0, this.length, "start");
     }
     if (pattern is String) {
       String other = pattern;
@@ -844,26 +844,10 @@ class _StringBase {
   }
 
   Iterable<Match> allMatches(String string, [int start = 0]) {
-    List<Match> result = new List<Match>();
-    int length = string.length;
-    int patternLength = this.length;
-    int startIndex = start;
-    while (true) {
-      int position = string.indexOf(this, startIndex);
-      if (position == -1) {
-        break;
-      }
-      result.add(new _StringMatch(position, string, this));
-      int endIndex = position + patternLength;
-      if (endIndex == length) {
-        break;
-      } else if (position == endIndex) {
-        ++startIndex;  // empty match, advance and restart
-      } else {
-        startIndex = endIndex;
-      }
+    if (start < 0 || start > string.length) {
+      throw new RangeError.range(start, 0, string.length, "start");
     }
-    return result;
+    return new _StringAllMatchesIterable(string, this, start);
   }
 
   Match matchAsPrefix(String string, [int start = 0]) {
@@ -1323,3 +1307,53 @@ class _StringMatch implements Match {
   final String input;
   final String pattern;
 }
+
+
+class _StringAllMatchesIterable extends Iterable<Match> {
+  final String _input;
+  final String _pattern;
+  final int _index;
+
+  _StringAllMatchesIterable(this._input, this._pattern, this._index);
+
+  Iterator<Match> get iterator =>
+      new _StringAllMatchesIterator(_input, _pattern, _index);
+
+  Match get first {
+    int index = _input.indexOf(_pattern, _index);
+    if (index >= 0) {
+      return new _StringMatch(index, _input, _pattern);
+    }
+    throw IterableElementError.noElement();
+  }
+}
+
+class _StringAllMatchesIterator implements Iterator<Match> {
+  final String _input;
+  final String _pattern;
+  int _index;
+  Match _current;
+
+  _StringAllMatchesIterator(this._input, this._pattern, this._index);
+
+  bool moveNext() {
+    if (_index + _pattern.length > _input.length) {
+      _current = null;
+      return false;
+    }
+    var index = _input.indexOf(_pattern, _index);
+    if (index < 0) {
+      _index = _input.length + 1;
+      _current = null;
+      return false;
+    }
+    int end = index + _pattern.length;
+    _current = new _StringMatch(index, _input, _pattern);
+    // Empty match, don't start at same location again.
+    if (end == _index) end++;
+    _index = end;
+    return true;
+  }
+
+  Match get current => _current;
+}
diff --git a/sdk/lib/_internal/js_runtime/lib/js_helper.dart b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
index fd53e61d99b..7cd2c69d730 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
@@ -57,7 +57,10 @@ import 'dart:_foreign_helper' show
 
 import 'dart:_interceptors';
 import 'dart:_internal' as _symbol_dev;
-import 'dart:_internal' show EfficientLength, MappedIterable;
+import 'dart:_internal' show
+    EfficientLength,
+    MappedIterable,
+    IterableElementError;
 
 import 'dart:_native_typed_data';
 
@@ -148,7 +151,7 @@ bool builtinIsSubtype(type, String other) {
 @ForceInline()
 bool isDartFunctionTypeRti(Object type) {
   return JS_BUILTIN('returns:bool;effects:none;depends:none',
-                    JsBuiltin.isGivenTypeRti, 
+                    JsBuiltin.isGivenTypeRti,
                     type,
                     JS_GET_NAME(JsGetName.FUNCTION_CLASS_TYPE_NAME));
 }
@@ -158,7 +161,7 @@ bool isDartFunctionTypeRti(Object type) {
 @ForceInline()
 bool isDartObjectTypeRti(type) {
   return JS_BUILTIN('returns:bool;effects:none;depends:none',
-                    JsBuiltin.isGivenTypeRti, 
+                    JsBuiltin.isGivenTypeRti,
                     type,
                     JS_GET_NAME(JsGetName.OBJECT_CLASS_TYPE_NAME));
 }
@@ -168,7 +171,7 @@ bool isDartObjectTypeRti(type) {
 @ForceInline()
 bool isNullTypeRti(type) {
   return JS_BUILTIN('returns:bool;effects:none;depends:none',
-                    JsBuiltin.isGivenTypeRti, 
+                    JsBuiltin.isGivenTypeRti,
                     type,
                     JS_GET_NAME(JsGetName.NULL_CLASS_TYPE_NAME));
 }
diff --git a/sdk/lib/_internal/js_runtime/lib/string_helper.dart b/sdk/lib/_internal/js_runtime/lib/string_helper.dart
index 51b696bc708..9ce91f8a179 100644
--- a/sdk/lib/_internal/js_runtime/lib/string_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/string_helper.dart
@@ -49,29 +49,58 @@ class StringMatch implements Match {
   final String pattern;
 }
 
-List<Match> allMatchesInStringUnchecked(String pattern, String string,
-                                        int startIndex) {
-  // Copied from StringBase.allMatches in
-  // /runtime/lib/string_base.dart
-  List<Match> result = new List<Match>();
-  int length = string.length;
-  int patternLength = pattern.length;
-  while (true) {
-    int position = stringIndexOfStringUnchecked(string, pattern, startIndex);
-    if (position == -1) {
-      break;
-    }
-    result.add(new StringMatch(position, string, pattern));
-    int endIndex = position + patternLength;
-    if (endIndex == length) {
-      break;
-    } else if (position == endIndex) {
-      ++startIndex;  // empty match, advance and restart
-    } else {
-      startIndex = endIndex;
+Iterable<Match> allMatchesInStringUnchecked(String pattern, String string,
+                                            int startIndex) {
+  return new _StringAllMatchesIterable(string, pattern, startIndex);
+}
+
+class _StringAllMatchesIterable extends Iterable<Match> {
+  final String _input;
+  final String _pattern;
+  final int _index;
+
+  _StringAllMatchesIterable(this._input, this._pattern, this._index);
+
+  Iterator<Match> get iterator =>
+      new _StringAllMatchesIterator(_input, _pattern, _index);
+
+  Match get first {
+    int index = stringIndexOfStringUnchecked(_input, _pattern, _index);
+    if (index >= 0) {
+      return new StringMatch(index, _input, _pattern);
     }
+    throw IterableElementError.noElement();
   }
-  return result;
+}
+
+class _StringAllMatchesIterator implements Iterator<Match> {
+  final String _input;
+  final String _pattern;
+  int _index;
+  Match _current;
+
+  _StringAllMatchesIterator(this._input, this._pattern, this._index);
+
+  bool moveNext() {
+    if (_index + _pattern.length > _input.length) {
+      _current = null;
+      return false;
+    }
+    var index = stringIndexOfStringUnchecked(_input, _pattern, _index);
+    if (index < 0) {
+      _index = _input.length + 1;
+      _current = null;
+      return false;
+    }
+    int end = index + _pattern.length;
+    _current = new StringMatch(index, _input, _pattern);
+    // Empty match, don't start at same location again.
+    if (end == _index) end++;
+    _index = end;
+    return true;
+  }
+
+  Match get current => _current;
 }
 
 stringContainsUnchecked(receiver, other, startIndex) {