diff --git a/src/scripts/scriptlib.fsx b/src/scripts/scriptlib.fsx
index cc797e305..5a7be7d2b 100644
--- a/src/scripts/scriptlib.fsx
+++ b/src/scripts/scriptlib.fsx
@@ -36,7 +36,7 @@ module Scripting =
 #if INTERACTIVE
     let argv = Microsoft.FSharp.Compiler.Interactive.Settings.fsi.CommandLineArgs |> Seq.skip 1 |> Seq.toArray

-    let getCmdLineArgOptional switchName = 
+    let getCmdLineArgOptional (switchName: string) =
         argv |> Array.filter(fun t -> t.StartsWith(switchName)) |> Array.map(fun t -> t.Remove(0, switchName.Length).Trim()) |> Array.tryHead 

     let getCmdLineArg switchName defaultValue =