diff --git a/mutannot.fsx b/mutannot.fsx
index 821447f..93c2c13 100755
--- a/mutannot.fsx
+++ b/mutannot.fsx
@@ -224,6 +224,26 @@ let tempRoot = Path.Combine(Path.GetTempPath(), $"fscheck-mutants.{Guid.NewGuid(
 let worktreePath = Path.Combine(tempRoot, "worktree")
 let patchPath = Path.Combine(tempRoot, "current.patch")
 
+let splitNullSeparated (text: string) =
+    text.Split('\000', StringSplitOptions.RemoveEmptyEntries)
+    |> Array.toList
+
+let repoRelativePath (path: string) =
+    path.Replace('/', Path.DirectorySeparatorChar)
+
+let listUntrackedFiles () =
+    let exitCode, stdout, stderr = captureProcess repoRoot "git" [ "ls-files"; "--others"; "--exclude-standard"; "-z" ]
+    if exitCode <> 0 then fail stderr
+    splitNullSeparated stdout
+
+let copyFileIntoWorktree (relativePath: string) =
+    let sourcePath = Path.Combine(repoRoot, repoRelativePath relativePath)
+    let destinationPath = Path.Combine(worktreePath, repoRelativePath relativePath)
+    let destinationDir = Path.GetDirectoryName destinationPath
+    if not (String.IsNullOrEmpty destinationDir) then
+        Directory.CreateDirectory(destinationDir) |> ignore
+    File.Copy(sourcePath, destinationPath, true)
+
 let cleanup () =
     if Directory.Exists worktreePath then
         let _ = captureProcess repoRoot "git" [ "worktree"; "remove"; "--force"; worktreePath ]
@@ -233,6 +253,7 @@ let cleanup () =
 
 let createWorktree () =
     Directory.CreateDirectory(tempRoot) |> ignore
+    let untrackedFiles = listUntrackedFiles ()
     let exitCode, diffText, stderr = captureProcess repoRoot "git" [ "diff"; "--binary"; "HEAD" ]
     if exitCode <> 0 then fail stderr
     File.WriteAllText(patchPath, diffText)
@@ -248,7 +269,14 @@ let createWorktree () =
         let exitCode4, _, stderr4 = captureProcess worktreePath "git" [ "apply"; patchPath ]
         if exitCode4 <> 0 then fail stderr4
 
-let testFilter mutation = $"FullyQualifiedName~{mutation.TestName}"
+    for relativePath in untrackedFiles do
+        copyFileIntoWorktree relativePath
+
+let fullyQualifiedTestName mutation =
+    let declaringType = mutation.DeclaringType.Replace('+', '.')
+    $"{declaringType}.{mutation.TestName}"
+
+let testFilter mutation = $"FullyQualifiedName={fullyQualifiedTestName mutation}"
 
 let runMutation (mutation: MutationCase) =
     let targetFile = Path.Combine(worktreePath, mutation.File.Replace('/', Path.DirectorySeparatorChar))