diff --git a/src/TestFramework/MSTest.Core/Assertions/Assert.cs b/src/TestFramework/MSTest.Core/Assertions/Assert.cs
index f930e80377..5e620a3919 100644
--- a/src/TestFramework/MSTest.Core/Assertions/Assert.cs
+++ b/src/TestFramework/MSTest.Core/Assertions/Assert.cs
@@ -14,12 +14,16 @@ namespace Microsoft.VisualStudio.TestTools.UnitTesting
     /// unit tests. If the condition being tested is not met, an exception
     /// is thrown.
     /// </summary>
-    public class Assert
+    public sealed class Assert
     {
         private static Assert that;
 
         #region Singleton constructor
 
+        private Assert()
+        {
+        }
+
         /// <summary>
         /// Gets the singleton instance of the Assert functionality.
         /// </summary>
diff --git a/src/TestFramework/MSTest.Core/Assertions/CollectionAssert.cs b/src/TestFramework/MSTest.Core/Assertions/CollectionAssert.cs
index a5e8a3535c..8388761be7 100644
--- a/src/TestFramework/MSTest.Core/Assertions/CollectionAssert.cs
+++ b/src/TestFramework/MSTest.Core/Assertions/CollectionAssert.cs
@@ -15,12 +15,16 @@ namespace Microsoft.VisualStudio.TestTools.UnitTesting
     /// with collections within unit tests. If the condition being tested is not
     /// met, an exception is thrown.
     /// </summary>
-    public class CollectionAssert
+    public sealed class CollectionAssert
     {
         private static CollectionAssert that;
 
         #region Singleton constructor
 
+        private CollectionAssert()
+        {
+        }
+
         /// <summary>
         /// Gets the singleton instance of the CollectionAssert functionality.
         /// </summary>
diff --git a/src/TestFramework/MSTest.Core/Assertions/StringAssert.cs b/src/TestFramework/MSTest.Core/Assertions/StringAssert.cs
index e0f3b5763f..e419efe17b 100644
--- a/src/TestFramework/MSTest.Core/Assertions/StringAssert.cs
+++ b/src/TestFramework/MSTest.Core/Assertions/StringAssert.cs
@@ -10,12 +10,16 @@ namespace Microsoft.VisualStudio.TestTools.UnitTesting
     /// <summary>
     /// The string assert.
     /// </summary>
-    public class StringAssert
+    public sealed class StringAssert
     {
         private static StringAssert that;
 
         #region Singleton constructor
 
+        private StringAssert()
+        {
+        }
+
         /// <summary>
         /// Gets the singleton instance of the CollectionAssert functionality.
         /// </summary>