diff --git a/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md b/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md
index 5bda852e8f46..82240b42625c 100644
--- a/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md
+++ b/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md
@@ -18,6 +18,7 @@
 * Fix for exponential runtime in CE builders when using nested implicit yields [PR #17096](https://github.com/dotnet/fsharp/pull/17096)
 * Fix several AND operator parser bugs and regressions ([Issue #16447](https://github.com/dotnet/fsharp/issues/16447), [Issue #17134](https://github.com/dotnet/fsharp/issues/17134), [Issue #16309](https://github.com/dotnet/fsharp/issues/16309), [PR #17113](https://github.com/dotnet/fsharp/pull/17113))
 * Treat exceptions as types in a namespace for graph based type checking ([Issue #17262](https://github.com/dotnet/fsharp/issues/17262), [PR #17268](https://github.com/dotnet/fsharp/pull/17268))
+* FS0243 - Unrecognized option: '--realsig-' #17561 ([Issue #17561](https://github.com/dotnet/fsharp/issues/17561), [PR #17268](https://github.com/dotnet/fsharp/pull/17562))
 
 ### Added
 
diff --git a/src/FSharp.Build/Fsc.fs b/src/FSharp.Build/Fsc.fs
index 74e499ad86e9..3394e8e97284 100644
--- a/src/FSharp.Build/Fsc.fs
+++ b/src/FSharp.Build/Fsc.fs
@@ -56,7 +56,7 @@ type public Fsc() as this =
     let mutable preferredUILang: string MaybeNull = null
     let mutable publicSign: bool = false
     let mutable provideCommandLineArgs: bool = false
-    let mutable realsig: bool = false
+    let mutable realsig: bool option = None
     let mutable references: ITaskItem[] = [||]
     let mutable referencePath: string MaybeNull = null
     let mutable refOnly: bool = false
@@ -196,10 +196,10 @@ type public Fsc() as this =
             builder.AppendSwitch("--optimize-")
 
         // realsig
-        if realsig then
-            builder.AppendSwitch("--realsig+")
-        else
-            builder.AppendSwitch("--realsig-")
+        match realsig with
+        | Some true -> builder.AppendSwitch("--realsig+")
+        | Some false -> builder.AppendSwitch("--realsig-")
+        | None -> ()
 
         // Tailcalls
         if not tailcalls then
@@ -539,8 +539,11 @@ type public Fsc() as this =
 
     // --realsig[+-]
     member _.RealSig
-        with get () = realsig
-        and set (b) = realsig <- b
+        with get () =
+            match realsig with
+            | Some true -> true
+            | _ -> false
+        and set (b) = realsig <- Some b
 
     // -r <string>: Reference an F# or .NET assembly.
     member _.References