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 60394d22e23..d4dad08b83a 100644
--- a/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md
+++ b/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md
@@ -19,6 +19,7 @@
 * 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 24952eceea1..0f4048a9280 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 = true
+    let mutable realsig: bool option = None
     let mutable references: ITaskItem[] = [||]
     let mutable referencePath: string MaybeNull = null
     let mutable refOnly: bool = false
@@ -197,10 +197,10 @@ 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
@@ -544,8 +544,11 @@ 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
diff --git a/vsintegration/tests/UnitTests/Tests.Build.fs b/vsintegration/tests/UnitTests/Tests.Build.fs
index bd1b88bcf6e..3c58fc3b63e 100644
--- a/vsintegration/tests/UnitTests/Tests.Build.fs
+++ b/vsintegration/tests/UnitTests/Tests.Build.fs
@@ -80,7 +80,6 @@ type Build() =
         AssertEqual ("--codepage:65001" + Environment.NewLine +
                      "--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -97,7 +96,6 @@ type Build() =
         AssertEqual ("-g" + Environment.NewLine +
                      "--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -114,7 +112,6 @@ type Build() =
         AssertEqual ("--debug:pdbonly" + Environment.NewLine +
                      "--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -133,7 +130,6 @@ type Build() =
                      "--define:FOO=3" + Environment.NewLine +
                      "--define:BAR=4" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -149,7 +145,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--nowarn:52,109" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -166,7 +161,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -182,7 +176,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--warnaserror-:52,109" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -199,7 +192,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--versionfile:src/version" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -217,7 +209,6 @@ type Build() =
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--doc:foo.xml" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -234,7 +225,6 @@ type Build() =
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--sig:foo.fsi" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -251,7 +241,6 @@ type Build() =
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--keyfile:key.txt" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -268,7 +257,6 @@ type Build() =
         AssertEqual ("--noframework" + Environment.NewLine +
                      "--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -284,7 +272,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize-" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -301,7 +288,6 @@ type Build() =
         // REVIEW we don't put the default, is that desired?
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -317,7 +303,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -336,7 +321,6 @@ type Build() =
         AssertEqual ("-o:oUt.dll" + Environment.NewLine +
                      "--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -352,7 +336,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--pdb:out.pdb" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -369,7 +352,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--platform:x64" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -386,7 +368,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--platform:x86" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -404,7 +385,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "-r:" + dll + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -422,7 +402,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--lib:c:\\sd\\staging\\tools\\nunit\\,c:\\Foo" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -440,7 +419,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--lib:c:\\program files,c:\\sd\\staging\\tools\\nunit,c:\\Foo" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -457,7 +435,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--resource:Foo.resources" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -476,7 +453,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva-" + Environment.NewLine +
@@ -495,7 +471,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--target:library" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -512,7 +487,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--target:winexe" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -529,7 +503,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--target:module" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -545,7 +518,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--utf8output" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -561,7 +533,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--win32res:foo.res" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -577,7 +548,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--win32manifest:foo.manifest" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
@@ -593,7 +563,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--highentropyva+" + Environment.NewLine +
@@ -608,7 +577,6 @@ type Build() =
         printfn "cmd=\"%s\"" cmd
         AssertEqual ("--compressmetadata" + Environment.NewLine +
                      "--optimize+" + Environment.NewLine +
-                     "--realsig+" + Environment.NewLine +
                      "--fullpaths" + Environment.NewLine +
                      "--flaterrors" + Environment.NewLine +
                      "--subsystemversion:6.02" + Environment.NewLine +
@@ -664,7 +632,6 @@ type Build() =
             "--sig:foo.fsi" + Environment.NewLine +
             "--keyfile:key.txt" + Environment.NewLine +
             "--optimize+" + Environment.NewLine +
-            "--realsig+" + Environment.NewLine +
             "--pdb:out.pdb" + Environment.NewLine +
             "--platform:anycpu" + Environment.NewLine +
             "--resource:MyRes.resources" + Environment.NewLine +
@@ -709,7 +676,6 @@ type Build() =
             "--sig:foo.fsi"
             "--keyfile:key.txt"
             "--optimize+"
-            "--realsig+"
             "--pdb:out.pdb"
             "--platform:anycpu"
             "--resource:MyRes.resources"
@@ -754,7 +720,6 @@ type Build() =
         let expected =
             "--compressmetadata" + Environment.NewLine +
             "--optimize+" + Environment.NewLine +
-            "--realsig+" + Environment.NewLine +
             "--nowarn:52,109,110,73,85" + Environment.NewLine +
             "--fullpaths" + Environment.NewLine +
             "--flaterrors" + Environment.NewLine +