diff --git a/sdk/lib/core/stopwatch.dart b/sdk/lib/core/stopwatch.dart
index 7d8ce334cd1..b446069f70c 100644
--- a/sdk/lib/core/stopwatch.dart
+++ b/sdk/lib/core/stopwatch.dart
@@ -63,6 +63,11 @@ abstract class Stopwatch {
    * Returns the frequency of the elapsed counter in Hz.
    */
   int get frequency;
+
+  /**
+   * Returns wether the [StopWatch] is currently running.
+   */
+  bool get isRunning;
 }
 
 class _StopwatchImpl implements Stopwatch {
@@ -77,14 +82,12 @@ class _StopwatchImpl implements Stopwatch {
   _StopwatchImpl() : _start = null, _stop = null {}
 
   void start() {
+    if (isRunning) return;
     if (_start == null) {
       // This stopwatch has never been started.
       _start = _now();
     } else {
-      if (_stop == null) {
-        return;
-      }
-      // Restarting this stopwatch. Prepend the elapsed time to the current
+      // Restart this stopwatch. Prepend the elapsed time to the current
       // start time.
       _start = _now() - (_stop - _start);
       _stop = null;
@@ -92,9 +95,7 @@ class _StopwatchImpl implements Stopwatch {
   }
 
   void stop() {
-    if (_start == null || _stop != null) {
-      return;
-    }
+    if (!isRunning) return;
     _stop = _now();
   }
 
@@ -127,6 +128,8 @@ class _StopwatchImpl implements Stopwatch {
 
   int get frequency => _frequency();
 
+  bool get isRunning => _start != null && _stop == null;
+
   external static int _frequency();
   external static int _now();
 }
diff --git a/tests/corelib/stopwatch_test.dart b/tests/corelib/stopwatch_test.dart
index b688ab3f377..2b9c1a6ae14 100644
--- a/tests/corelib/stopwatch_test.dart
+++ b/tests/corelib/stopwatch_test.dart
@@ -8,7 +8,9 @@ library stopwatch_test;
 
 class StopwatchTest {
   static bool checkTicking(Stopwatch sw) {
+    Expect.isFalse(sw.isRunning);
     sw.start();
+    Expect.isTrue(sw.isRunning);
     for (int i = 0; i < 10000; i++) {
       int.parse(i.toString());
       if (sw.elapsedTicks > 0) {
@@ -20,10 +22,12 @@ class StopwatchTest {
 
   static bool checkStopping(Stopwatch sw) {
     sw.stop();
+    Expect.isFalse(sw.isRunning);
     int v1 = sw.elapsedTicks;
     Expect.isTrue(v1 > 0);  // Expect a non-zero elapsed time.
     Stopwatch sw2 = new Stopwatch();  // Used for verification.
     sw2.start();
+    Expect.isTrue(sw2.isRunning);
     int sw2LastElapsed = 0;
     for (int i = 0; i < 100000; i++) {
       int.parse(i.toString());
@@ -46,7 +50,9 @@ class StopwatchTest {
 
   static checkRestart() {
     Stopwatch sw = new Stopwatch();
+    Expect.isFalse(sw.isRunning);
     sw.start();
+    Expect.isTrue(sw.isRunning);
     for (int i = 0; i < 100000; i++) {
       int.parse(i.toString());
       if (sw.elapsedTicks > 0) {
@@ -54,8 +60,10 @@ class StopwatchTest {
       }
     }
     sw.stop();
+    Expect.isFalse(sw.isRunning);
     int initial = sw.elapsedTicks;
     sw.start();
+    Expect.isTrue(sw.isRunning);
     for (int i = 0; i < 100000; i++) {
       int.parse(i.toString());
       if (sw.elapsedTicks > initial) {
@@ -63,12 +71,15 @@ class StopwatchTest {
       }
     }
     sw.stop();
+    Expect.isFalse(sw.isRunning);
     Expect.isTrue(sw.elapsedTicks > initial);
   }
 
   static checkReset() {
     Stopwatch sw = new Stopwatch();
+    Expect.isFalse(sw.isRunning);
     sw.start();
+    Expect.isTrue(sw.isRunning);
     for (int i = 0; i < 100000; i++) {
       int.parse(i.toString());
       if (sw.elapsedTicks > 0) {
@@ -76,9 +87,12 @@ class StopwatchTest {
       }
     }
     sw.stop();
+    Expect.isFalse(sw.isRunning);
     sw.reset();
+    Expect.isFalse(sw.isRunning);
     Expect.equals(0, sw.elapsedTicks);
     sw.start();
+    Expect.isTrue(sw.isRunning);
     for (int i = 0; i < 100000; i++) {
       int.parse(i.toString());
       if (sw.elapsedTicks > 0) {
@@ -86,6 +100,7 @@ class StopwatchTest {
       }
     }
     sw.reset();
+    Expect.isTrue(sw.isRunning);
     for (int i = 0; i < 100000; i++) {
       int.parse(i.toString());
       if (sw.elapsedTicks > 0) {
@@ -93,6 +108,7 @@ class StopwatchTest {
       }
     }
     sw.stop();
+    Expect.isFalse(sw.isRunning);
     Expect.isTrue(sw.elapsedTicks > 0);
   }