diff --git a/SystemExtensions/Collections/AVLTree.cs b/SystemExtensions/Collections/AVLTree.cs
index 638095c..dd1dff6 100644
--- a/SystemExtensions/Collections/AVLTree.cs
+++ b/SystemExtensions/Collections/AVLTree.cs
@@ -14,7 +14,7 @@ namespace SystemExtensions.Collections
     /// </summary>
     /// <typeparam name="T">Provided type.</typeparam>
     [Serializable]
-    public class AVLTree<T> : ICollection<T> where T : IComparable<T>
+    public sealed class AVLTree<T> : ICollection<T> where T : IComparable<T>
     {
         #region Fields
         [Serializable]
diff --git a/SystemExtensions/Collections/BinaryHeap.cs b/SystemExtensions/Collections/BinaryHeap.cs
index 398588e..5315ba8 100644
--- a/SystemExtensions/Collections/BinaryHeap.cs
+++ b/SystemExtensions/Collections/BinaryHeap.cs
@@ -12,7 +12,7 @@ namespace SystemExtensions.Collections
     /// </summary>
     /// <typeparam name="T">Provided type.</typeparam>
     [Serializable]
-    public class BinaryHeap<T> : IEnumerable<T> where T : IComparable<T>
+    public sealed class BinaryHeap<T> : IEnumerable<T> where T : IComparable<T>
     {
         #region Fields
         T[] items;
diff --git a/SystemExtensions/Collections/FibonacciHeap.cs b/SystemExtensions/Collections/FibonacciHeap.cs
index d364727..6272838 100644
--- a/SystemExtensions/Collections/FibonacciHeap.cs
+++ b/SystemExtensions/Collections/FibonacciHeap.cs
@@ -12,7 +12,7 @@ namespace SystemExtensions.Collections
     /// </summary>
     /// <typeparam name="T">Provided type</typeparam>
     [Serializable]
-    public class FibonacciHeap<T> : IEnumerable<T> where T : IComparable<T>
+    public sealed class FibonacciHeap<T> : IEnumerable<T> where T : IComparable<T>
     {
         #region Fields
         private FibonacciNode<T> root;
@@ -462,7 +462,7 @@ namespace SystemExtensions.Collections
         #endregion
     }
     [Serializable]
-    internal class FibonacciNode<T>
+    internal sealed class FibonacciNode<T>
     {
         #region Fields
         private FibonacciNode<T> previous;
diff --git a/SystemExtensions/Collections/PriorityQueue.cs b/SystemExtensions/Collections/PriorityQueue.cs
index d4f6b21..3d94c48 100644
--- a/SystemExtensions/Collections/PriorityQueue.cs
+++ b/SystemExtensions/Collections/PriorityQueue.cs
@@ -13,7 +13,7 @@ namespace SystemExtensions.Collections
     /// </summary>
     /// <typeparam name="T">Provided type.</typeparam>
     [Serializable]
-    public class PriorityQueue<T> : IQueue<T> where T : IComparable<T>
+    public sealed class PriorityQueue<T> : IQueue<T> where T : IComparable<T>
     {
         #region Fields
         private BinaryHeap<T> binaryHeap;
diff --git a/SystemExtensions/Collections/SkipList.cs b/SystemExtensions/Collections/SkipList.cs
index 66963cd..6ee1e23 100644
--- a/SystemExtensions/Collections/SkipList.cs
+++ b/SystemExtensions/Collections/SkipList.cs
@@ -12,7 +12,7 @@ namespace SystemExtensions.Collections
     /// </summary>
     /// <typeparam name="T">Provided type.</typeparam>
     [Serializable]
-    public class SkipList<T> : ICollection<T> where T : IComparable<T>
+    public sealed class SkipList<T> : ICollection<T> where T : IComparable<T>
     {
         #region Fields
         [Serializable]
diff --git a/SystemExtensions/Collections/Treap.cs b/SystemExtensions/Collections/Treap.cs
index 3615634..72c7a60 100644
--- a/SystemExtensions/Collections/Treap.cs
+++ b/SystemExtensions/Collections/Treap.cs
@@ -12,7 +12,7 @@ namespace SystemExtensions.Collections
     /// </summary>
     /// <typeparam name="T">Provided type.</typeparam>
     [Serializable]
-    public class Treap<T> : ICollection<T> where T : IComparable<T>
+    public sealed class Treap<T> : ICollection<T> where T : IComparable<T>
     {
         #region Fields
         [Serializable]
diff --git a/SystemExtensions/Threading/PriorityThreadPool.cs b/SystemExtensions/Threading/PriorityThreadPool.cs
index dd9febc..4f98085 100644
--- a/SystemExtensions/Threading/PriorityThreadPool.cs
+++ b/SystemExtensions/Threading/PriorityThreadPool.cs
@@ -13,7 +13,7 @@ namespace SystemExtensions.Threading
     /// Features both an automated algorithm to calibrate the number of active threads and a Constructor for constructing
     /// a threadpool manually, without the auto-managed pool algorithm.
     /// </summary>
-    public class PriorityThreadPool : IDisposable
+    public sealed class PriorityThreadPool : IDisposable
     {
         private class QueueEntry : IComparable<QueueEntry>
         {