diff --git a/src/fsharp/FSharp.Compiler.Service.ProjectCracker/ProjectCracker.fs b/src/fsharp/FSharp.Compiler.Service.ProjectCracker/ProjectCracker.fs
index 93adc72d28..baf8102279 100644
--- a/src/fsharp/FSharp.Compiler.Service.ProjectCracker/ProjectCracker.fs
+++ b/src/fsharp/FSharp.Compiler.Service.ProjectCracker/ProjectCracker.fs
@@ -20,7 +20,7 @@ type ProjectCracker =
             let referencedProjects = Array.map (fun (a, b) -> a, convert b) opts.ReferencedProjectOptions
             
             let sourceFiles, otherOptions = 
-                opts.Options |> Array.partition (fun x -> Path.GetExtension(x).ToLower() = ".fs")
+                opts.Options |> Array.partition (fun x -> x.IndexOfAny(Path.GetInvalidPathChars()) = -1 && Path.GetExtension(x).ToLower() = ".fs")
             
             let sepChar = Path.DirectorySeparatorChar