diff --git a/Source/Tracking/Internal/ObservedProgression.cs b/Source/Tracking/Internal/ObservedProgression.cs
index aab0d8d..2906387 100644
--- a/Source/Tracking/Internal/ObservedProgression.cs
+++ b/Source/Tracking/Internal/ObservedProgression.cs
@@ -40,7 +40,7 @@ namespace Nuclex.Support.Tracking {
 
     /// <summary>Immediately releases all resources owned by the object</summary>
     public void Dispose() {
-      disconnectEvents();
+      asyncDisconnectEvents();
     }
 
     /// <summary>Weighted progression being observed</summary>
@@ -57,11 +57,15 @@ namespace Nuclex.Support.Tracking {
     /// <param name="sender">Progression that has ended</param>
     /// <param name="e">Not used</param>
     private void asyncEnded(object sender, EventArgs e) {
+      ReportDelegate endedCallback = this.endedCallback;
+      ReportDelegate progressUpdateCallback = this.progressUpdateCallback;
+
+      asyncDisconnectEvents(); // We don't need those anymore!
+
       this.progress = 1.0f;
+      progressUpdateCallback();
 
-      disconnectEvents(); // We don't need those anymore!
-
-      this.progressUpdateCallback();
+      endedCallback();
     }
 
     /// <summary>Called when the progress of the observed progression changes</summary>
@@ -74,7 +78,7 @@ namespace Nuclex.Support.Tracking {
     }
 
     /// <summary>Unscribes from all events of the observed progression</summary>
-    private void disconnectEvents() {
+    private void asyncDisconnectEvents() {
 
       // Make use of the double check locking idiom to avoid the costly lock when
       // the events have already been unsubscribed
diff --git a/Source/Tracking/Progression.cs b/Source/Tracking/Progression.cs
index 05a20cd..b8c24c0 100644
--- a/Source/Tracking/Progression.cs
+++ b/Source/Tracking/Progression.cs
@@ -113,15 +113,18 @@ namespace Nuclex.Support.Tracking {
     ///   seperately.
     /// </remarks>
     protected virtual void OnAsyncEnded() {
+ 
+      // Make sure the progression is not ended more than once. By guaranteeing that
+      // a progression can only be ended once, we allow users of this class to
+      // skip some safeguards against notifications arriving twice.
+      lock(this.syncRoot) {
 
-      // TODO: Find a way around this. Interlocked.Exchange would be best!
-      // We do not lock here since we require this method to be called only once
-      // in the object's lifetime. If someone really badly wanted to break this
-      // he'd probably have a one-in-a-million chance of getting through.
-      if(this.ended)
-        throw new InvalidOperationException("The progression has already been ended");
+        if(this.ended)
+          throw new InvalidOperationException("The progression has already been ended");
 
-      this.ended = true;
+        this.ended = true;
+
+      }
 
       // Doesn't need a lock. If another thread wins the race and creates the event
       // after we just saw it being null, it would be created in an already set
diff --git a/Source/Tracking/SetProgression.Test.cs b/Source/Tracking/SetProgression.Test.cs
index f39658f..2d014f7 100644
--- a/Source/Tracking/SetProgression.Test.cs
+++ b/Source/Tracking/SetProgression.Test.cs
@@ -104,9 +104,7 @@ namespace Nuclex.Support.Tracking {
     public void TestSummedProgress() {
       SetProgression<TestProgression> testSetProgression =
         new SetProgression<TestProgression>(
-          new TestProgression[] {
-            new TestProgression(), new TestProgression()
-          }
+          new TestProgression[] { new TestProgression(), new TestProgression() }
         );
 
       ISetProgressionSubscriber mockedSubscriber = mockSubscriber(testSetProgression);
@@ -184,9 +182,7 @@ namespace Nuclex.Support.Tracking {
     public void TestEndedEvent() {
       SetProgression<TestProgression> testSetProgression =
         new SetProgression<TestProgression>(
-          new TestProgression[] {
-            new TestProgression(), new TestProgression()
-          }
+          new TestProgression[] { new TestProgression(), new TestProgression() }
         );
 
       ISetProgressionSubscriber mockedSubscriber = mockSubscriber(testSetProgression);
diff --git a/Source/Tracking/SetProgression.cs b/Source/Tracking/SetProgression.cs
index c2ce6da..bc0f2c9 100644
--- a/Source/Tracking/SetProgression.cs
+++ b/Source/Tracking/SetProgression.cs
@@ -8,14 +8,16 @@ namespace Nuclex.Support.Tracking {
 
   /// <summary>Forms a single progression from a set of progressions</summary>
   /// <typeparam name="ProgressionType">Type of progressions to manage as a set</typeparam>
-  public class SetProgression<ProgressionType> : Progression
+  public class SetProgression<ProgressionType> : Progression, IDisposable
     where ProgressionType : Progression {
 
     /// <summary>Performs common initialization for the public constructors</summary>
     private SetProgression() {
       this.childs = new List<ObservedProgression<ProgressionType>>();
+
       this.asyncProgressUpdatedDelegate =
         new ObservedProgression<ProgressionType>.ReportDelegate(asyncProgressUpdated);
+
       this.asyncEndedDelegate =
         new ObservedProgression<ProgressionType>.ReportDelegate(asyncEnded);
     }
@@ -71,6 +73,23 @@ namespace Nuclex.Support.Tracking {
 
     }
 
+    /// <summary>Immediately releases all resources owned by the object</summary>
+    public void Dispose() {
+
+      if(this.childs != null) {
+
+        // Dispose all the observed progressions, disconnecting the events from the
+        // actual progressions so the GC can more easily collect this class
+        for(int index = 0; index < this.childs.Count; ++index)
+          this.childs[index].Dispose();
+
+        this.childs = null;
+        this.wrapper = null;
+
+      }
+
+    }
+
     /// <summary>Childs contained in the progression set</summary>
     public IList<WeightedProgression<ProgressionType>> Childs {
       get {
@@ -120,10 +139,13 @@ namespace Nuclex.Support.Tracking {
     /// </summary>
     private void asyncEnded() {
 
+      // If there's still at least one progression going, don't report that
+      // the SetProgression has finished yet.
       for(int index = 0; index < this.childs.Count; ++index)
         if(!this.childs[index].WeightedProgression.Progression.Ended)
           return;
 
+      // All child progressions have ended, so the set has now ended as well
       OnAsyncEnded();
 
     }