diff --git a/src/J2N/Text/CharArrayCharSequence.cs b/src/J2N/Text/CharArrayCharSequence.cs
index 72e46a68..a8856cbb 100644
--- a/src/J2N/Text/CharArrayCharSequence.cs
+++ b/src/J2N/Text/CharArrayCharSequence.cs
@@ -29,7 +29,7 @@ namespace J2N.Text
     /// <summary>
     /// A wrapper class that represents a <see cref="T:char[]"/> and implements <see cref="ICharSequence"/>.
     /// </summary>
-    public class CharArrayCharSequence : ICharSequence,
+    public sealed class CharArrayCharSequence : ICharSequence,
         IComparable<ICharSequence>, IComparable,
         IComparable<string>, IComparable<StringBuilder>, IComparable<char[]>,
         IEquatable<ICharSequence>,
diff --git a/src/J2N/Text/StringBuilderCharSequence.cs b/src/J2N/Text/StringBuilderCharSequence.cs
index 9b7cc061..ac03f0a9 100644
--- a/src/J2N/Text/StringBuilderCharSequence.cs
+++ b/src/J2N/Text/StringBuilderCharSequence.cs
@@ -28,7 +28,7 @@ namespace J2N.Text
     /// <summary>
     /// A wrapper class that represents a <see cref="System.Text.StringBuilder"/> and implements <see cref="ICharSequence"/>.
     /// </summary>
-    public class StringBuilderCharSequence : ICharSequence, IAppendable, 
+    public sealed class StringBuilderCharSequence : ICharSequence, IAppendable,
         IComparable<ICharSequence>, IComparable,
         IComparable<string>, IComparable<StringBuilder>, IComparable<char[]>,
         IEquatable<ICharSequence>,
diff --git a/src/J2N/Text/StringCharSequence.cs b/src/J2N/Text/StringCharSequence.cs
index 3c47f972..713003da 100644
--- a/src/J2N/Text/StringCharSequence.cs
+++ b/src/J2N/Text/StringCharSequence.cs
@@ -28,7 +28,7 @@ namespace J2N.Text
     /// <summary>
     /// A wrapper class that represents a <see cref="string"/> and implements <see cref="ICharSequence"/>.
     /// </summary>
-    public class StringCharSequence : ICharSequence, 
+    public sealed class StringCharSequence : ICharSequence,
         IComparable<ICharSequence>, IComparable,
         IComparable<string>, IComparable<StringBuilder>, IComparable<char[]>,
         IEquatable<ICharSequence>,