diff --git a/src/ImageSharp.Formats.Tiff/AssemblyInfo.cs b/src/ImageSharp.Formats.Tiff/AssemblyInfo.cs
new file mode 100644
index 000000000..4d1cbfe55
--- /dev/null
+++ b/src/ImageSharp.Formats.Tiff/AssemblyInfo.cs
@@ -0,0 +1,11 @@
+// <copyright file="AssemblyInfo.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+using System.Reflection;
+using System.Resources;
+using System.Runtime.CompilerServices;
+
+// Ensure the internals can be tested.
+[assembly: InternalsVisibleTo("ImageSharp.Formats.Tiff.Tests")]
\ No newline at end of file
diff --git a/src/ImageSharp.Formats.Tiff/TiffTags.cs b/src/ImageSharp.Formats.Tiff/TiffTags.cs
index db4087d58..41721fb1d 100644
--- a/src/ImageSharp.Formats.Tiff/TiffTags.cs
+++ b/src/ImageSharp.Formats.Tiff/TiffTags.cs
@@ -8,7 +8,7 @@ namespace ImageSharp.Formats
     /// <summary>
     /// Constants representing tag IDs in the Tiff file-format.
     /// </summary>
-    public class TiffTags
+    internal class TiffTags
     {
         // Section 8: Baseline Fields
 
diff --git a/src/ImageSharp.Formats.Tiff/TiffType.cs b/src/ImageSharp.Formats.Tiff/TiffType.cs
index 1bb7f6cfb..b98236c0f 100644
--- a/src/ImageSharp.Formats.Tiff/TiffType.cs
+++ b/src/ImageSharp.Formats.Tiff/TiffType.cs
@@ -8,7 +8,7 @@ namespace ImageSharp.Formats
     /// <summary>
     /// Enumeration representing the data types understood by the Tiff file-format.
     /// </summary>
-    public enum TiffType
+    internal enum TiffType
     {
         Byte = 1,
         Ascii = 2,
diff --git a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/ITiffGenDataSource.cs b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/ITiffGenDataSource.cs
index 33bf99924..1c8a485b9 100644
--- a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/ITiffGenDataSource.cs
+++ b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/ITiffGenDataSource.cs
@@ -11,7 +11,7 @@ namespace ImageSharp.Tests
     /// <summary>
     /// An interface for any class within the Tiff generator that produces data to be included in the file.
     /// </summary>
-    public interface ITiffGenDataSource
+    internal interface ITiffGenDataSource
     {
         IEnumerable<TiffGenDataBlock> GetData(bool isLittleEndian);
     }
diff --git a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenDataBlock.cs b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenDataBlock.cs
index bbce12054..6a91dbbcc 100644
--- a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenDataBlock.cs
+++ b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenDataBlock.cs
@@ -12,7 +12,7 @@ namespace ImageSharp.Tests
     /// A utility data structure to represent an independent block of data in a Tiff file.
     /// These may be located in any order within a Tiff file.
     /// </summary>
-    public class TiffGenDataBlock
+    internal class TiffGenDataBlock
     {
         public TiffGenDataBlock(byte[] bytes)
         {
diff --git a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenDataReference.cs b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenDataReference.cs
index ec4c0c5df..90cacb23d 100644
--- a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenDataReference.cs
+++ b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenDataReference.cs
@@ -11,7 +11,7 @@ namespace ImageSharp.Tests
     /// <summary>
     /// A utility data structure to represent a reference from one block of data to another in a Tiff file.
     /// </summary>
-    public class TiffGenDataReference
+    internal class TiffGenDataReference
     {
         public TiffGenDataReference(byte[] bytes, int offset)
         {
diff --git a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenEntry.cs b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenEntry.cs
index 4f0ff868b..df61b4d8a 100644
--- a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenEntry.cs
+++ b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenEntry.cs
@@ -14,7 +14,7 @@ namespace ImageSharp.Tests
     /// <summary>
     /// A utility data structure to represent Tiff IFD entries in unit tests.
     /// </summary>
-    public abstract class TiffGenEntry : ITiffGenDataSource
+    internal abstract class TiffGenEntry : ITiffGenDataSource
     {
         private TiffGenEntry(ushort tag, TiffType type)
         {
diff --git a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenExtensions.cs b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenExtensions.cs
index 87ba62121..21c3b0844 100644
--- a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenExtensions.cs
+++ b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenExtensions.cs
@@ -12,7 +12,7 @@ namespace ImageSharp.Tests
     /// <summary>
     /// A utility class for generating in-memory Tiff files for use in unit tests.
     /// </summary>
-    public static class TiffGenExtensions
+    internal static class TiffGenExtensions
     {
         public static byte[] ToBytes(this ITiffGenDataSource dataSource, bool isLittleEndian)
         {
diff --git a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenHeader.cs b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenHeader.cs
index 95322dc66..b28ceedc2 100644
--- a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenHeader.cs
+++ b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenHeader.cs
@@ -12,7 +12,7 @@ namespace ImageSharp.Tests
     /// <summary>
     /// A utility data structure to represent a Tiff file-header.
     /// </summary>
-    public class TiffGenHeader : ITiffGenDataSource
+    internal class TiffGenHeader : ITiffGenDataSource
     {
         public TiffGenHeader()
         {
diff --git a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenIfd.cs b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenIfd.cs
index 2e745df36..c26a0f199 100644
--- a/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenIfd.cs
+++ b/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffGenIfd.cs
@@ -12,7 +12,7 @@ namespace ImageSharp.Tests
     /// <summary>
     /// A utility data structure to represent Tiff IFDs in unit tests.
     /// </summary>
-    public class TiffGenIfd : ITiffGenDataSource
+    internal class TiffGenIfd : ITiffGenDataSource
     {
         public TiffGenIfd()
         {