diff --git a/src/projects/EnsureThat/Internals/ExceptionFactory.cs b/src/projects/EnsureThat/IExceptionFactory.cs
similarity index 72%
rename from src/projects/EnsureThat/Internals/ExceptionFactory.cs
rename to src/projects/EnsureThat/IExceptionFactory.cs
index 8005370..c08150c 100644
--- a/src/projects/EnsureThat/Internals/ExceptionFactory.cs
+++ b/src/projects/EnsureThat/IExceptionFactory.cs
@@ -1,11 +1,17 @@
 using System;
 using JetBrains.Annotations;
-
 using NotNullAttribute = System.Diagnostics.CodeAnalysis.NotNullAttribute;
 
-namespace EnsureThat.Internals
+namespace EnsureThat
 {
-    internal sealed class ExceptionFactory : IExceptionFactory
+    public interface IExceptionFactory
+    {
+        Exception ArgumentException([NotNull] string defaultMessage, string paramName, OptsFn optsFn = null);
+        Exception ArgumentNullException([NotNull] string defaultMessage, string paramName, OptsFn optsFn = null);
+        Exception ArgumentOutOfRangeException<TValue>([NotNull] string defaultMessage, string paramName, TValue value, OptsFn optsFn = null);
+    }
+
+    public sealed class ExceptionFactory : IExceptionFactory
     {
         [return: NotNull]
         [Pure]
@@ -15,6 +21,9 @@ public Exception ArgumentException(string defaultMessage, string paramName, Opts
             {
                 var opts = optsFn(new EnsureOptions());
 
+                if (opts.CustomExceptionFactory != null)
+                    return opts.CustomExceptionFactory(defaultMessage, paramName);
+
                 if (opts.CustomException != null)
                     return opts.CustomException;
 
@@ -54,6 +63,9 @@ public Exception ArgumentOutOfRangeException<TValue>(string defaultMessage, stri
             {
                 var opts = optsFn(new EnsureOptions());
 
+                if (opts.CustomExceptionFactory != null)
+                    return opts.CustomExceptionFactory(defaultMessage, paramName);
+
                 if (opts.CustomException != null)
                     return opts.CustomException;
 
diff --git a/src/projects/EnsureThat/Internals/IExceptionFactory.cs b/src/projects/EnsureThat/Internals/IExceptionFactory.cs
deleted file mode 100644
index ce41ba3..0000000
--- a/src/projects/EnsureThat/Internals/IExceptionFactory.cs
+++ /dev/null
@@ -1,12 +0,0 @@
-using System;
-using JetBrains.Annotations;
-
-namespace EnsureThat.Internals
-{
-    public interface IExceptionFactory
-    {
-        Exception ArgumentException([NotNull] string defaultMessage, string paramName, OptsFn optsFn = null);
-        Exception ArgumentNullException([NotNull] string defaultMessage, string paramName, OptsFn optsFn = null);
-        Exception ArgumentOutOfRangeException<TValue>([NotNull] string defaultMessage, string paramName, TValue value, OptsFn optsFn = null);
-    }
-}
diff --git a/src/tests/UnitTests/ExceptionFactoryTests.cs b/src/tests/UnitTests/ExceptionFactoryTests.cs
new file mode 100644
index 0000000..236d358
--- /dev/null
+++ b/src/tests/UnitTests/ExceptionFactoryTests.cs
@@ -0,0 +1,145 @@
+using System;
+using System.Collections.Generic;
+using EnsureThat;
+using FluentAssertions;
+using Xunit;
+
+namespace UnitTests
+{
+    public class ExceptionFactoryTests : UnitTestBase
+    {
+        private const string DefaultMessage = "54a170d6997c400487c177768f72aa7a";
+        private const string CustomMessage = "3b3e6082d4c1482fbc775abc11a2e415";
+        private const string DummyValue = "61927e885db34e08b9a7211c7eb74c36";
+        private readonly Exception _exceptionFactoryException = new KeyNotFoundException();
+        private readonly Exception _customException = new("036859e6693848b199575feffe17bd46");
+        private readonly ExceptionFactory _sut = new();
+
+        [Fact]
+        public void ArgumentException_UsesDefaults_WhenNoOptionsAreProvided()
+            => _sut.ArgumentException(
+                    DefaultMessage,
+                    ParamName)
+                .Should()
+                .BeEquivalentTo(new ArgumentException(DefaultMessage, ParamName));
+
+        [Fact]
+        public void ArgumentException_UsesExceptionFactory_WhenOptionsAlsoContainsCustomExceptionAndCustomMessage()
+            => _sut.ArgumentException(
+                    DefaultMessage,
+                    ParamName,
+                    o => o
+                        .WithMessage(CustomMessage)
+                        .WithException(_customException)
+                        .WithExceptionFactory((_, __) => _exceptionFactoryException))
+                .Should()
+                .Be(_exceptionFactoryException);
+
+        [Fact]
+        public void ArgumentException_UsesCustomException_WhenOptionsAlsoContainsCustomMessage()
+            => _sut.ArgumentException(
+                    DefaultMessage,
+                    ParamName,
+                    o => o
+                        .WithMessage(CustomMessage)
+                        .WithException(_customException))
+                .Should()
+                .Be(_customException);
+
+        [Fact]
+        public void ArgumentException_UsesCustomMessage_WhenOptionsHasNoOtherConfig()
+            => _sut.ArgumentException(
+                    DefaultMessage,
+                    ParamName,
+                    o => o
+                        .WithMessage(CustomMessage))
+                .Should()
+                .BeEquivalentTo(new ArgumentException(CustomMessage, ParamName));
+
+        [Fact]
+        public void ArgumentNullException_UsesDefaults_WhenNoOptionsAreProvided()
+            => _sut.ArgumentNullException(
+                    DefaultMessage,
+                    ParamName)
+                .Should()
+                .BeEquivalentTo(new ArgumentNullException(ParamName, DefaultMessage));
+
+        [Fact]
+        public void ArgumentNullException_UsesExceptionFactory_WhenOptionsAlsoContainsCustomExceptionAndCustomMessage()
+            => _sut.ArgumentNullException(
+                    DefaultMessage,
+                    ParamName,
+                    o => o
+                        .WithMessage(CustomMessage)
+                        .WithException(_customException)
+                        .WithExceptionFactory((_, __) => _exceptionFactoryException))
+                .Should()
+                .Be(_exceptionFactoryException);
+
+        [Fact]
+        public void ArgumentNullException_UsesCustomException_WhenOptionsAlsoContainsCustomMessage()
+            => _sut.ArgumentNullException(
+                    DefaultMessage,
+                    ParamName,
+                    o => o
+                        .WithMessage(CustomMessage)
+                        .WithException(_customException))
+                .Should()
+                .Be(_customException);
+
+        [Fact]
+        public void ArgumentNullException_UsesCustomMessage_WhenOptionsHasNoOtherConfig()
+            => _sut.ArgumentNullException(
+                    DefaultMessage,
+                    ParamName,
+                    o => o
+                        .WithMessage(CustomMessage))
+                .Should()
+                .BeEquivalentTo(new ArgumentNullException(ParamName, CustomMessage));
+
+        [Fact]
+        public void ArgumentOutOfRangeException_UsesDefaults_WhenNoOptionsAreProvided()
+            => _sut.ArgumentOutOfRangeException(
+                    DefaultMessage,
+                    ParamName,
+                    DummyValue)
+                .Should()
+                .BeEquivalentTo(new ArgumentOutOfRangeException(ParamName, DummyValue, DefaultMessage));
+
+        [Fact]
+        public void ArgumentOutOfRangeException_UsesExceptionFactory_WhenOptionsAlsoContainsCustomExceptionAndCustomMessage()
+            => _sut.ArgumentOutOfRangeException(
+                    DefaultMessage,
+                    ParamName,
+                    DummyValue,
+                    o => o
+                        .WithMessage(CustomMessage)
+                        .WithException(_customException)
+                        .WithExceptionFactory((_, __) => _exceptionFactoryException))
+                .Should()
+                .Be(_exceptionFactoryException);
+
+        [Fact]
+        public void ArgumentOutOfRangeException_UsesCustomException_WhenOptionsAlsoContainsCustomMessage()
+            => _sut.ArgumentOutOfRangeException(
+                    DefaultMessage,
+                    ParamName,
+                    DummyValue,
+                    o => o
+                        .WithMessage(CustomMessage)
+                        .WithException(_customException))
+                .Should()
+                .Be(_customException);
+
+        [Fact]
+        public void ArgumentOutOfRangeException_UsesCustomMessage_WhenOptionsHasNoOtherConfig()
+            => _sut.ArgumentOutOfRangeException(
+                    DefaultMessage,
+                    ParamName,
+                    DummyValue,
+                    o => o
+                        .WithMessage(CustomMessage))
+                .Should()
+                .BeEquivalentTo(new ArgumentOutOfRangeException(ParamName, DummyValue, CustomMessage));
+    }
+}