diff --git a/Assets/PatchKit Patcher/Scripts/AppUpdater/Commands/InstallDiffCommand.cs b/Assets/PatchKit Patcher/Scripts/AppUpdater/Commands/InstallDiffCommand.cs
index 090a7d55..901d69f9 100644
--- a/Assets/PatchKit Patcher/Scripts/AppUpdater/Commands/InstallDiffCommand.cs	
+++ b/Assets/PatchKit Patcher/Scripts/AppUpdater/Commands/InstallDiffCommand.cs	
@@ -533,7 +533,8 @@ private void ProcessModifiedFiles(string packageDirPath, string suffix, Temporar
 
         private long GetTotalSizeModifiedFiles()
         {
-            IEnumerable<string> modifiedFiles = _diffSummary.ModifiedFiles.Where(f => !_diffSummary.UnchangedFiles.Contains(f));
+            var unchangedFiles = new HashSet<string>(_diffSummary.UnchangedFiles);
+            var modifiedFiles = new HashSet<string>(_diffSummary.ModifiedFiles).Where(f => !unchangedFiles.Contains(f));
             return _contentSummary.Files.Where(f => modifiedFiles.Contains(f.Path)).Sum(f => f.Size);
         }
         
diff --git a/Assets/PatchKit Patcher/Scripts/Version.cs b/Assets/PatchKit Patcher/Scripts/Version.cs
index 37fe65fa..e6f6eff9 100644
--- a/Assets/PatchKit Patcher/Scripts/Version.cs	
+++ b/Assets/PatchKit Patcher/Scripts/Version.cs	
@@ -5,7 +5,7 @@ public static class Version
         public const int Major = 3;
         public const int Minor = 17;
         public const int Patch = 12;
-        public const int Hotfix = 0;
+        public const int Hotfix = 1;
 
         public static string Value
         {
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0e1fdf89..a5fa0dd7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [3.17.12.1]
+### Fixed
+- Crash during patching operation
+
 ## [3.17.12.0]
 ### Fixed
 - Displaying the progress bar for patching files for large files