diff --git a/AltCover.Engine/Tasks.fs b/AltCover.Engine/Tasks.fs
index b76c58a9..2abd0e15 100644
--- a/AltCover.Engine/Tasks.fs
+++ b/AltCover.Engine/Tasks.fs
@@ -357,8 +357,8 @@ type RunSettings() =
                     Justification = "Unit test accessor")>]
   member val internal MessageIO: (string -> unit) option = None with get, set
 
-  member val internal GetTempFileName: Func<string> =
-    Func<string>(Path.GetTempFileName) with get, set
+  member val internal GetTempFileName: (unit -> string) =
+    Path.GetTempFileName with get, set
 
   override self.Execute() =
     let signal =
@@ -373,7 +373,7 @@ type RunSettings() =
       |> sprintf "Settings Before: %s"
       |> signal
 
-    let tempFile = self.GetTempFileName.Invoke()
+    let tempFile = self.GetTempFileName()
 
     try
       let settings =
diff --git a/AltCover.Tests/Tests3.fs b/AltCover.Tests/Tests3.fs
index 5db6e05d..c6a4cbdd 100644
--- a/AltCover.Tests/Tests3.fs
+++ b/AltCover.Tests/Tests3.fs
@@ -4464,14 +4464,14 @@ module AltCoverTests3 =
         .GetProperty("GetTempFileName", BindingFlags.Instance ||| BindingFlags.NonPublic)
 
     let basic =
-      temper.GetValue(subject) :?> Func<string>
+      temper.GetValue(subject) :?> (unit -> string)
 
     let badge =
       (fun () ->
-        let t1 = basic.Invoke()
+        let t1 = basic ()
         Path.Combine(Path.GetDirectoryName t1, "altcover.test." + Path.GetFileName(t1)))
 
-    temper.SetValue(subject, Func<string>(badge))
+    temper.SetValue(subject, badge)
     subject
 
   [<Test>]