diff --git a/rxjava-core/src/main/java/rx/subscriptions/CompositeSubscription.java b/rxjava-core/src/main/java/rx/subscriptions/CompositeSubscription.java
index a94fd047ae..8fd5739fb9 100644
--- a/rxjava-core/src/main/java/rx/subscriptions/CompositeSubscription.java
+++ b/rxjava-core/src/main/java/rx/subscriptions/CompositeSubscription.java
@@ -38,6 +38,8 @@ public class CompositeSubscription implements Subscription {
      */
     private AtomicBoolean unsubscribed = new AtomicBoolean(false);
     private final ConcurrentHashMap<Subscription, Boolean> subscriptions = new ConcurrentHashMap<Subscription, Boolean>();
+    
+    private final Object guard = new Object();
 
     public CompositeSubscription(List<Subscription> subscriptions) {
         for (Subscription s : subscriptions) {
@@ -87,19 +89,32 @@ public boolean isUnsubscribed() {
         return unsubscribed.get();
     }
 
-    public synchronized void add(Subscription s) {
-        if (unsubscribed.get()) {
-            s.unsubscribe();
-        } else {
-            subscriptions.put(s, Boolean.TRUE);
+    public void add(Subscription s) {
+        Subscription q = null;
+        synchronized (guard) {
+            if (unsubscribed.get()) {
+                q = s;
+            } else {
+                subscriptions.put(s, Boolean.TRUE);
+            }
+        }
+        if (q != null) {
+            q.unsubscribe();
         }
     }
 
     @Override
-    public synchronized void unsubscribe() {
-        if (unsubscribed.compareAndSet(false, true)) {
+    public void unsubscribe() {
+        List<Subscription> toUnsubscribe = null;
+        synchronized (guard) {
+            if (unsubscribed.compareAndSet(false, true)) {
+                toUnsubscribe = new ArrayList<Subscription>(subscriptions.keySet());
+                subscriptions.clear();
+            }
+        }
+        if (toUnsubscribe != null) {
             Collection<Throwable> es = null;
-            for (Subscription s : subscriptions.keySet()) {
+            for (Subscription s : toUnsubscribe) {
                 try {
                     s.unsubscribe();
                 } catch (Throwable e) {
diff --git a/rxjava-core/src/main/java/rx/subscriptions/MultipleAssignmentSubscription.java b/rxjava-core/src/main/java/rx/subscriptions/MultipleAssignmentSubscription.java
index 74ed285f77..ff12f2f3a8 100644
--- a/rxjava-core/src/main/java/rx/subscriptions/MultipleAssignmentSubscription.java
+++ b/rxjava-core/src/main/java/rx/subscriptions/MultipleAssignmentSubscription.java
@@ -15,7 +15,6 @@
  */
 package rx.subscriptions;
 
-import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
 
 import rx.Observable;
@@ -28,33 +27,45 @@
  */
 public class MultipleAssignmentSubscription implements Subscription {
 
-    private final AtomicBoolean unsubscribed = new AtomicBoolean(false);
-    private AtomicReference<Subscription> subscription = new AtomicReference<Subscription>();
-
+    private final AtomicReference<Subscription> inner = new AtomicReference<Subscription>();
+    private static final Subscription UNSUBSCRIBED = new Subscription() {
+        @Override
+        public void unsubscribe() {
+        }
+    };
     public boolean isUnsubscribed() {
-        return unsubscribed.get();
+        return inner.get() == UNSUBSCRIBED;
     }
 
     @Override
-    public synchronized void unsubscribe() {
-        unsubscribed.set(true);
-        Subscription s = getSubscription();
+    public void unsubscribe() {
+        Subscription s = inner.getAndSet(UNSUBSCRIBED);
         if (s != null) {
             s.unsubscribe();
         }
-
     }
 
-    public synchronized void setSubscription(Subscription s) {
-        if (unsubscribed.get()) {
-            s.unsubscribe();
-        } else {
-            subscription.set(s);
-        }
+    public void setSubscription(Subscription s) {
+        do {
+            Subscription r = inner.get();
+            if (r == UNSUBSCRIBED) {
+                s.unsubscribe();
+                return;
+            } else {
+                if (inner.compareAndSet(r, s)) {
+                    return;
+                }
+            }
+        } while (true);
     }
 
     public Subscription getSubscription() {
-        return subscription.get();
+        Subscription r = inner.get();
+        // don't leak the unsubscription sentinel
+        if (r == UNSUBSCRIBED) {
+            return Subscriptions.empty();
+        }
+        return r;
     }
 
 }
diff --git a/rxjava-core/src/test/java/rx/subscriptions/MultipleAssignmentSubscriptionTest.java b/rxjava-core/src/test/java/rx/subscriptions/MultipleAssignmentSubscriptionTest.java
new file mode 100644
index 0000000000..8e4f782be2
--- /dev/null
+++ b/rxjava-core/src/test/java/rx/subscriptions/MultipleAssignmentSubscriptionTest.java
@@ -0,0 +1,68 @@
+/**
+ * Copyright 2013 Netflix, Inc.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package rx.subscriptions;
+
+import junit.framework.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import rx.Subscription;
+import static rx.subscriptions.Subscriptions.create;
+import rx.util.functions.Action0;
+
+public class MultipleAssignmentSubscriptionTest {
+    Action0 unsubscribe;
+    Subscription s;
+    @Before
+    public void before() {
+         unsubscribe = mock(Action0.class);
+         s = create(unsubscribe);
+    }
+    @Test
+    public void testNoUnsubscribeWhenReplaced() {
+        MultipleAssignmentSubscription mas = new MultipleAssignmentSubscription();
+        
+        mas.setSubscription(s);
+        mas.setSubscription(null);
+        mas.unsubscribe();        
+        
+        verify(unsubscribe, never()).call();
+        
+    }
+    @Test
+    public void testUnsubscribeWhenParentUnsubscribes() {
+        MultipleAssignmentSubscription mas = new MultipleAssignmentSubscription();
+        mas.setSubscription(s);
+        mas.unsubscribe();
+        mas.unsubscribe();
+        
+        verify(unsubscribe, times(1)).call();
+        
+        Assert.assertEquals(true, mas.isUnsubscribed());
+    }
+    @Test
+    public void testUnsubscribedDoesntLeakSentinel() {
+        MultipleAssignmentSubscription mas = new MultipleAssignmentSubscription();
+
+        mas.setSubscription(s);
+        mas.unsubscribe();
+        
+        Assert.assertEquals(true, mas.getSubscription() == Subscriptions.empty());
+    }
+}