diff --git a/src/ImageProcessor/Common/Extensions/ByteExtensions.cs b/src/ImageProcessor/Common/Extensions/ByteExtensions.cs
index 958326f176..d11132801f 100644
--- a/src/ImageProcessor/Common/Extensions/ByteExtensions.cs
+++ b/src/ImageProcessor/Common/Extensions/ByteExtensions.cs
@@ -29,7 +29,7 @@ namespace ImageProcessor
         public static byte[] ToArrayByBitsLength(this byte[] bytes, int bits)
         {
             Guard.NotNull(bytes, "bytes");
-            Guard.GreaterThan(bits, 0, "bits");
+            Guard.MustBeGreaterThan(bits, 0, "bits");
 
             byte[] result;
 
diff --git a/src/ImageProcessor/Common/Helpers/Guard.cs b/src/ImageProcessor/Common/Helpers/Guard.cs
index 438831fa0a..d832e1b82c 100644
--- a/src/ImageProcessor/Common/Helpers/Guard.cs
+++ b/src/ImageProcessor/Common/Helpers/Guard.cs
@@ -11,11 +11,12 @@
 namespace ImageProcessor
 {
     using System;
-    using System.Globalization;
+    using System.Diagnostics;
 
     /// <summary>
     /// Provides methods to protect against invalid parameters.
     /// </summary>
+    [DebuggerStepThrough]
     internal static class Guard
     {
         /// <summary>
@@ -70,7 +71,7 @@ namespace ImageProcessor
 
             if (string.IsNullOrWhiteSpace(target))
             {
-                throw new ArgumentException("String parameter cannot be null or empty and cannot contain only blanks.", parameterName);
+                throw new ArgumentException("Value cannot be null or empty and cannot contain only blanks.", parameterName);
             }
         }
 
@@ -85,7 +86,7 @@ namespace ImageProcessor
         /// <exception cref="ArgumentException">
         /// <paramref name="value"/> is greater than the maximum value.
         /// </exception>
-        public static void LessThan<TValue>(TValue value, TValue max, string parameterName) where TValue : IComparable<TValue>
+        public static void MustBeLessThan<TValue>(TValue value, TValue max, string parameterName) where TValue : IComparable<TValue>
         {
             if (value.CompareTo(max) >= 0)
             {
@@ -106,7 +107,7 @@ namespace ImageProcessor
         /// <exception cref="ArgumentException">
         /// <paramref name="value"/> is greater than the maximum value.
         /// </exception>
-        public static void LessEquals<TValue>(TValue value, TValue max, string parameterName) where TValue : IComparable<TValue>
+        public static void MustBeLessThanOrEqualTo<TValue>(TValue value, TValue max, string parameterName) where TValue : IComparable<TValue>
         {
             if (value.CompareTo(max) > 0)
             {
@@ -127,7 +128,7 @@ namespace ImageProcessor
         /// <exception cref="ArgumentException">
         /// <paramref name="value"/> is less than the minimum value.
         /// </exception>
-        public static void GreaterThan<TValue>(TValue value, TValue min, string parameterName) where TValue : IComparable<TValue>
+        public static void MustBeGreaterThan<TValue>(TValue value, TValue min, string parameterName) where TValue : IComparable<TValue>
         {
             if (value.CompareTo(min) <= 0)
             {
@@ -148,7 +149,7 @@ namespace ImageProcessor
         /// <exception cref="ArgumentException">
         /// <paramref name="value"/> is less than the minimum value.
         /// </exception>
-        public static void GreaterEquals<TValue>(TValue value, TValue min, string parameterName) where TValue : IComparable<TValue>
+        public static void MustBeGreaterThanOrEqualTo<TValue>(TValue value, TValue min, string parameterName) where TValue : IComparable<TValue>
         {
             if (value.CompareTo(min) < 0)
             {
@@ -170,7 +171,7 @@ namespace ImageProcessor
         /// <exception cref="ArgumentException">
         /// <paramref name="value"/> is less than the minimum value of greater than the maximum value.
         /// </exception>
-        public static void BetweenEquals<TValue>(TValue value, TValue min, TValue max, string parameterName) where TValue : IComparable<TValue>
+        public static void MustBeBetweenOrEqualTo<TValue>(TValue value, TValue min, TValue max, string parameterName) where TValue : IComparable<TValue>
         {
             if (value.CompareTo(min) < 0 || value.CompareTo(max) > 0)
             {
diff --git a/src/ImageProcessor/Formats/Gif/LzwDecoder.cs b/src/ImageProcessor/Formats/Gif/LzwDecoder.cs
index 1c3d5d28ba..4d6cfd4fb9 100644
--- a/src/ImageProcessor/Formats/Gif/LzwDecoder.cs
+++ b/src/ImageProcessor/Formats/Gif/LzwDecoder.cs
@@ -56,7 +56,7 @@ namespace ImageProcessor.Formats
         /// <returns>The decoded and uncompressed array.</returns>
         public byte[] DecodePixels(int width, int height, int dataSize)
         {
-            Guard.LessThan(dataSize, int.MaxValue, nameof(dataSize));
+            Guard.MustBeLessThan(dataSize, int.MaxValue, nameof(dataSize));
 
             // The resulting index table.
             byte[] pixels = new byte[width * height];
diff --git a/src/ImageProcessor/Formats/Gif/Quantizer/OctreeQuantizer.cs b/src/ImageProcessor/Formats/Gif/Quantizer/OctreeQuantizer.cs
index 5844e3d878..a7ebe8ec3b 100644
--- a/src/ImageProcessor/Formats/Gif/Quantizer/OctreeQuantizer.cs
+++ b/src/ImageProcessor/Formats/Gif/Quantizer/OctreeQuantizer.cs
@@ -57,8 +57,8 @@ namespace ImageProcessor.Formats
         public OctreeQuantizer(int maxColors, int maxColorBits)
             : base(false)
         {
-            Guard.LessEquals(maxColors, 255, "maxColors");
-            Guard.BetweenEquals(maxColorBits, 1, 8, "maxColorBits");
+            Guard.MustBeLessThanOrEqualTo(maxColors, 255, "maxColors");
+            Guard.MustBeBetweenOrEqualTo(maxColorBits, 1, 8, "maxColorBits");
 
             // Construct the Octree
             this.octree = new Octree(maxColorBits);
diff --git a/src/ImageProcessor/Formats/Gif/Quantizer/QuantizedImage.cs b/src/ImageProcessor/Formats/Gif/Quantizer/QuantizedImage.cs
index 627eee2acd..5738f9e887 100644
--- a/src/ImageProcessor/Formats/Gif/Quantizer/QuantizedImage.cs
+++ b/src/ImageProcessor/Formats/Gif/Quantizer/QuantizedImage.cs
@@ -42,8 +42,8 @@ namespace ImageProcessor.Formats
         /// </summary>
         public QuantizedImage(int width, int height, Bgra[] palette, byte[] pixels)
         {
-            Guard.GreaterThan(width, 0, nameof(width));
-            Guard.GreaterThan(height, 0, nameof(height));
+            Guard.MustBeGreaterThan(width, 0, nameof(width));
+            Guard.MustBeGreaterThan(height, 0, nameof(height));
             Guard.NotNull(palette, nameof(palette));
             Guard.NotNull(pixels, nameof(pixels));
 
diff --git a/src/ImageProcessor/Formats/Jpg/LibJpeg/BitStream.cs b/src/ImageProcessor/Formats/Jpg/LibJpeg/BitStream.cs
index 2bdaae68c2..9c2128bcd9 100644
--- a/src/ImageProcessor/Formats/Jpg/LibJpeg/BitStream.cs
+++ b/src/ImageProcessor/Formats/Jpg/LibJpeg/BitStream.cs
@@ -129,7 +129,7 @@ namespace ImageProcessor.Formats
         /// </returns>
         public virtual int Read(int bitCount)
         {
-            Guard.LessEquals(this.Tell() + bitCount, this.BitsAllocated(), "bitCount");
+            Guard.MustBeLessThanOrEqualTo(this.Tell() + bitCount, this.BitsAllocated(), "bitCount");
             return this.ReadBits(bitCount);
         }
 
@@ -150,7 +150,7 @@ namespace ImageProcessor.Formats
 
             const int MaxBitsInStorage = sizeof(int) * BitsInByte;
 
-            Guard.LessEquals(bitCount, MaxBitsInStorage, "bitCount");
+            Guard.MustBeLessThanOrEqualTo(bitCount, MaxBitsInStorage, "bitCount");
 
             for (int i = 0; i < bitCount; ++i)
             {
@@ -251,7 +251,7 @@ namespace ImageProcessor.Formats
             // This stream is then divided into 8-bit bytes, high-order bit first. 
             // Thus, codes can straddle byte boundaries arbitrarily. After the EOD marker (code value 257), 
             // any leftover bits in the final byte are set to 0.
-            Guard.BetweenEquals(bitsCount, 0, 32, "bitsCount");
+            Guard.MustBeBetweenOrEqualTo(bitsCount, 0, 32, "bitsCount");
 
             if (bitsCount == 0)
             {
@@ -338,7 +338,7 @@ namespace ImageProcessor.Formats
         /// </param>
         private void SeekSet(int position)
         {
-            Guard.GreaterEquals(position, 0, "position");
+            Guard.MustBeGreaterThanOrEqualTo(position, 0, "position");
 
             int byteDisplacement = position / BitsInByte;
             this.stream.Seek(byteDisplacement, SeekOrigin.Begin);
@@ -356,7 +356,7 @@ namespace ImageProcessor.Formats
         private void SeekCurrent(int position)
         {
             int result = this.Tell() + position;
-            Guard.BetweenEquals(position, 0, this.BitsAllocated(), "position");
+            Guard.MustBeBetweenOrEqualTo(position, 0, this.BitsAllocated(), "position");
 
             this.SeekSet(result);
         }
diff --git a/src/ImageProcessor/ImageBase.cs b/src/ImageProcessor/ImageBase.cs
index 517ac184f8..0773d63e85 100644
--- a/src/ImageProcessor/ImageBase.cs
+++ b/src/ImageProcessor/ImageBase.cs
@@ -40,8 +40,8 @@ namespace ImageProcessor
         /// </exception>
         protected ImageBase(int width, int height)
         {
-            Guard.GreaterThan(width, 0, "width");
-            Guard.GreaterThan(height, 0, "height");
+            Guard.MustBeGreaterThan(width, 0, "width");
+            Guard.MustBeGreaterThan(height, 0, "height");
 
             this.Width = width;
             this.Height = height;
diff --git a/src/ImageProcessor/Properties/AssemblyInfo.cs b/src/ImageProcessor/Properties/AssemblyInfo.cs
index a4372aa743..fbdbb3a814 100644
--- a/src/ImageProcessor/Properties/AssemblyInfo.cs
+++ b/src/ImageProcessor/Properties/AssemblyInfo.cs
@@ -28,3 +28,6 @@ using System.Runtime.InteropServices;
 // [assembly: AssemblyVersion("1.0.*")]
 [assembly: AssemblyVersion("3.0.0.0")]
 [assembly: AssemblyFileVersion("3.0.0.0")]
+
+// Ensure the internals can be tested.
+[assembly: InternalsVisibleTo("ImageProcessor.Tests")]
diff --git a/tests/ImageProcessor.Tests/Helpers/GuardTests.cs b/tests/ImageProcessor.Tests/Helpers/GuardTests.cs
new file mode 100644
index 0000000000..e983b7dbe8
--- /dev/null
+++ b/tests/ImageProcessor.Tests/Helpers/GuardTests.cs
@@ -0,0 +1,209 @@
+// --------------------------------------------------------------------------------------------------------------------
+// <copyright file="GuardTests.cs" company="James South">
+//   Copyright © James South and contributors.
+//   Licensed under the Apache License, Version 2.0.
+// </copyright>
+// <summary>
+//   Tests the <see cref="Guard" /> helper.
+// </summary>
+// --------------------------------------------------------------------------------------------------------------------
+
+namespace ImageProcessor.Tests.Helpers
+{
+    using System;
+    using System.Diagnostics.CodeAnalysis;
+
+    using Xunit;
+
+    /// <summary>
+    /// Tests the <see cref="Guard"/> helper.
+    /// </summary>
+    public class GuardTests
+    {
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.NotNull"/> method throws when the argument is null.
+        /// </summary>
+        [Fact]
+        public void NotNullThrowsWhenArgIsNull()
+        {
+            Assert.Throws<ArgumentNullException>(() => Guard.NotNull(null, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.NotNull"/> method throws when the argument name is empty.
+        /// </summary>
+        [Fact]
+        public void NotNullThrowsWhenArgNameEmpty()
+        {
+            Assert.Throws<ArgumentNullException>(() => Guard.NotNull(null, string.Empty));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.NotEmpty"/> method throws when the argument is empty.
+        /// </summary>
+        [Fact]
+        [SuppressMessage("StyleCop.CSharp.ReadabilityRules", "SA1122:UseStringEmptyForEmptyStrings", Justification = "Reviewed. Suppression is OK here.")]
+        public void NotEmptyThrowsWhenEmpty()
+        {
+            Assert.Throws<ArgumentException>(() => Guard.NotNullOrEmpty("", string.Empty));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.NotEmpty"/> method throws when the argument is whitespace.
+        /// </summary>
+        [Fact]
+        public void NotEmptyThrowsWhenWhitespace()
+        {
+            Assert.Throws<ArgumentException>(() => Guard.NotNullOrEmpty(" ", string.Empty));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.NotEmpty"/> method throws when the argument name is null.
+        /// </summary>
+        [Fact]
+        public void NotEmptyThrowsWhenParameterNameNull()
+        {
+            Assert.Throws<ArgumentNullException>(() => Guard.NotNullOrEmpty(null, null));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThan"/> method throws when the argument is greater.
+        /// </summary>
+        [Fact]
+        public void LessThanThrowsWhenArgIsGreater()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeLessThan(1, 0, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThan"/> method throws when the argument is equal.
+        /// </summary>
+        [Fact]
+        public void LessThanThrowsWhenArgIsEqual()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeLessThan(1, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThanOrEqual"/> method throws when the argument is greater.
+        /// </summary>
+        [Fact]
+        public void LessThanOrEqualToThrowsWhenArgIsGreater()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeLessThanOrEqualTo(1, 0, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThanOrEqual"/> method does not throw when the argument 
+        /// is less.
+        /// </summary>
+        [Fact]
+        public void LessThanOrEqualToDoesNotThrowWhenArgIsLess()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeLessThanOrEqualTo(0, 1, "foo"));
+            Assert.Null(ex);
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThanOrEqual"/> method does not throw when the argument 
+        /// is equal.
+        /// </summary>
+        [Fact]
+        public void LessThanOrEqualToDoesNotThrowWhenArgIsEqual()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeLessThanOrEqualTo(1, 1, "foo"));
+            Assert.Equal(1, 1);
+            Assert.Null(ex);
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThan"/> method throws when the argument is greater.
+        /// </summary>
+        [Fact]
+        public void GreaterThanThrowsWhenArgIsLess()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeGreaterThan(0, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThan"/> method throws when the argument is greater.
+        /// </summary>
+        [Fact]
+        public void GreaterThanThrowsWhenArgIsEqual()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeGreaterThan(1, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThan"/> method throws when the argument name is greater.
+        /// </summary>
+        [Fact]
+        public void GreaterThanOrEqualToThrowsWhenArgIsLess()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeGreaterThanOrEqualTo(0, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThanOrEqual"/> method does not throw when the argument 
+        /// is less.
+        /// </summary>
+        [Fact]
+        public void GreaterThanOrEqualToDoesNotThrowWhenArgIsGreater()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeGreaterThanOrEqualTo(1, 0, "foo"));
+            Assert.Null(ex);
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThanOrEqual"/> method does not throw when the argument 
+        /// is equal.
+        /// </summary>
+        [Fact]
+        public void GreaterThanOrEqualToDoesNotThrowWhenArgIsEqual()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeGreaterThanOrEqualTo(1, 1, "foo"));
+            Assert.Equal(1, 1);
+            Assert.Null(ex);
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeBetweenOrEqualTo"/> method throws when the argument is less.
+        /// </summary>
+        [Fact]
+        public void BetweenOrEqualToThrowsWhenArgIsLess()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeBetweenOrEqualTo(-2, -1, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeBetweenOrEqualTo"/> method throws when the argument is greater.
+        /// </summary>
+        [Fact]
+        public void BetweenOrEqualToThrowsWhenArgIsGreater()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeBetweenOrEqualTo(2, -1, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeBetweenOrEqualTo"/> method does not throw when the argument 
+        /// is equal.
+        /// </summary>
+        [Fact]
+        public void BetweenOrEqualToDoesNotThrowWhenArgIsEqual()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeBetweenOrEqualTo(1, 1, 1, "foo"));
+            Assert.Null(ex);
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeBetweenOrEqualTo"/> method does not throw when the argument 
+        /// is equal.
+        /// </summary>
+        [Fact]
+        public void BetweenOrEqualToDoesNotThrowWhenArgIsBetween()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeBetweenOrEqualTo(0, -1, 1, "foo"));
+            Assert.Null(ex);
+        }
+    }
+}
diff --git a/tests/ImageProcessor.Tests/ImageProcessor.Tests.csproj b/tests/ImageProcessor.Tests/ImageProcessor.Tests.csproj
index 893425d4dd..ec75612e25 100644
--- a/tests/ImageProcessor.Tests/ImageProcessor.Tests.csproj
+++ b/tests/ImageProcessor.Tests/ImageProcessor.Tests.csproj
@@ -54,6 +54,7 @@
     <Compile Include="Colors\ColorConversionTests.cs" />
     <Compile Include="Colors\ColorTests.cs" />
     <Compile Include="Formats\EncoderDecoderTests.cs" />
+    <Compile Include="Helpers\GuardTests.cs" />
     <Compile Include="Numerics\RectangleTests.cs" />
     <Compile Include="Numerics\PointTests.cs" />
     <Compile Include="Numerics\SizeTests.cs" />
@@ -79,4 +80,4 @@
     <Error Condition="!Exists('..\..\packages\xunit.core.2.0.0\build\portable-net45+win+wpa81+wp80+monotouch+monoandroid+Xamarin.iOS\xunit.core.props')" Text="$([System.String]::Format('$(ErrorText)', '..\..\packages\xunit.core.2.0.0\build\portable-net45+win+wpa81+wp80+monotouch+monoandroid+Xamarin.iOS\xunit.core.props'))" />
     <Error Condition="!Exists('..\..\packages\xunit.runner.visualstudio.2.0.0\build\net20\xunit.runner.visualstudio.props')" Text="$([System.String]::Format('$(ErrorText)', '..\..\packages\xunit.runner.visualstudio.2.0.0\build\net20\xunit.runner.visualstudio.props'))" />
   </Target>
-</Project>
+</Project>
\ No newline at end of file