diff --git a/Wabbajack.Lib/Installer.cs b/Wabbajack.Lib/Installer.cs
index cbedd716..abf0a280 100644
--- a/Wabbajack.Lib/Installer.cs
+++ b/Wabbajack.Lib/Installer.cs
@@ -98,7 +98,7 @@ namespace Wabbajack.Lib
 
         public void Install()
         {
-
+            ValidateGameESMs();
             ValidateModlist.RunValidation(ModList);
 
             VirtualFileSystem.Clean();
@@ -121,7 +121,8 @@ namespace Wabbajack.Lib
 
             var game = GameRegistry.Games[ModList.GameType];
 
-            GameFolder = game.GameLocation;
+            if (GameFolder == null)
+                GameFolder = game.GameLocation;
 
             if (GameFolder == null)
             {
@@ -163,6 +164,21 @@ namespace Wabbajack.Lib
             //AskToEndorse();
         }
 
+        private void ValidateGameESMs()
+        {
+            foreach (var esm in ModList.Directives.OfType<CleanedESM>().ToList())
+            {
+                var filename = Path.GetFileName(esm.To);
+                var game_file = Path.Combine(GameFolder, "Data", filename);
+                Utils.Log($"Validating {filename}");
+                var hash = game_file.FileHash();
+                if (hash != esm.SourceESMHash)
+                {
+                    Utils.Error("Game ESM hash doesn't match, is the ESM already cleaned? Please verify your local game files.");
+                }
+            }
+        }
+
         private void AskToEndorse()
         {
             var mods = ModList.Archives
@@ -308,8 +324,9 @@ namespace Wabbajack.Lib
             var to_file = Path.Combine(Outputfolder, directive.To);
             Status($"Patching {filename}");
             using (var output = File.OpenWrite(to_file))
+            using (var input = File.OpenRead(game_file))
             {
-                BSDiff.Apply(File.OpenRead(game_file), () => new MemoryStream(patch_data), output);
+                BSDiff.Apply(input, () => new MemoryStream(patch_data), output);
             }
         }
 
diff --git a/Wabbajack.Test/ACompilerTest.cs b/Wabbajack.Test/ACompilerTest.cs
index 9a0eb223..78dd2fe9 100644
--- a/Wabbajack.Test/ACompilerTest.cs
+++ b/Wabbajack.Test/ACompilerTest.cs
@@ -10,7 +10,7 @@ using Wabbajack.Lib;
 
 namespace Wabbajack.Test
 {
-    public abstract class ACompilerTest
+    public abstract class  ACompilerTest
     {
         public TestContext TestContext { get; set; }
         protected TestUtils utils { get; set; }
diff --git a/Wabbajack.Test/SanityTests.cs b/Wabbajack.Test/SanityTests.cs
index 19115113..210f5aaf 100644
--- a/Wabbajack.Test/SanityTests.cs
+++ b/Wabbajack.Test/SanityTests.cs
@@ -1,13 +1,15 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Runtime;
-using Alphaleonis.Win32.Filesystem;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Microsoft.VisualStudio.TestTools.UnitTesting.Logging;
 using VFS;
 using Wabbajack.Common;
 using Wabbajack.Lib;
+using File = Alphaleonis.Win32.Filesystem.File;
+using Path = Alphaleonis.Win32.Filesystem.Path;
 
 namespace Wabbajack.Test
 {
@@ -32,6 +34,33 @@ namespace Wabbajack.Test
             utils.VerifyInstalledFile(mod, @"Data\scripts\test.pex");
         }
 
+        [TestMethod]
+        public void CleanedESMTest()
+        {
+
+            var profile = utils.AddProfile();
+            var mod = utils.AddMod("Cleaned ESMs");
+            var update_esm = utils.AddModFile(mod, @"Update.esm", 10);
+
+            utils.Configure();
+
+            var game_file = Path.Combine(utils.GameFolder, "Data", "Update.esm");
+            utils.GenerateRandomFileData(game_file, 20);
+
+            var modlist = CompileAndInstall(profile);
+
+            utils.VerifyInstalledFile(mod, @"Update.esm");
+
+            var compiler = ConfigureAndRunCompiler(profile);
+
+            // Update the file and verify that it throws an error.
+            utils.GenerateRandomFileData(game_file, 20);
+            var exception = Assert.ThrowsException<Exception>(() => Install(compiler));
+            Assert.AreEqual(exception.Message, "Game ESM hash doesn't match, is the ESM already cleaned? Please verify your local game files.");
+
+
+        }
+
         [TestMethod]
         public void UnmodifiedInlinedFilesArePulledFromArchives()
         {
diff --git a/Wabbajack.Test/TestUtils.cs b/Wabbajack.Test/TestUtils.cs
index d84811b2..95316f55 100644
--- a/Wabbajack.Test/TestUtils.cs
+++ b/Wabbajack.Test/TestUtils.cs
@@ -53,7 +53,7 @@ namespace Wabbajack.Test
             });
 
             Directory.CreateDirectory(DownloadsFolder);
-            Directory.CreateDirectory(GameFolder);
+            Directory.CreateDirectory(Path.Combine(GameFolder, "Data"));
 
             Profiles.Do(profile =>
             {
@@ -92,6 +92,17 @@ namespace Wabbajack.Test
         /// <param name="random_fill"></param>
         /// <returns></returns>
         public string AddModFile(string mod_name, string path, int random_fill=128)
+        {
+
+
+            var full_path = Path.Combine(ModsFolder, mod_name, path);
+            Directory.CreateDirectory(Path.GetDirectoryName(full_path));
+
+            GenerateRandomFileData(full_path, random_fill);
+            return full_path;
+        }
+
+        public void GenerateRandomFileData(string full_path, int random_fill)
         {
             byte[] bytes = new byte[0];
             if (random_fill != 0)
@@ -100,10 +111,7 @@ namespace Wabbajack.Test
                 RNG.NextBytes(bytes);
             }
 
-            var full_path = Path.Combine(ModsFolder, mod_name, path);
-            Directory.CreateDirectory(Path.GetDirectoryName(full_path));
             File.WriteAllBytes(full_path, bytes);
-            return full_path;
         }
 
         public void Dispose()