diff --git a/docs/release-notes/.FSharp.Compiler.Service/10.0.300.md b/docs/release-notes/.FSharp.Compiler.Service/10.0.300.md
index 471abbfb982..4a9351dd9d1 100644
--- a/docs/release-notes/.FSharp.Compiler.Service/10.0.300.md
+++ b/docs/release-notes/.FSharp.Compiler.Service/10.0.300.md
@@ -1,5 +1,6 @@
 ### Fixed
 
+* Fix strong name signature size to align with Roslyn for public signing ([PR #19242](https://github.com/dotnet/fsharp/pull/19242))
 * Fixed Find All References not correctly finding active pattern cases in signature files. ([Issue #19173](https://github.com/dotnet/fsharp/issues/19173), [Issue #14969](https://github.com/dotnet/fsharp/issues/14969), [PR #19252](https://github.com/dotnet/fsharp/pull/19252))
 * Fixed Rename not correctly handling operators containing `.` (e.g., `-.-`). ([Issue #17221](https://github.com/dotnet/fsharp/issues/17221), [Issue #14057](https://github.com/dotnet/fsharp/issues/14057), [PR #19252](https://github.com/dotnet/fsharp/pull/19252))
 * Fixed Find All References not correctly applying `#line` directive remapping. ([Issue #9928](https://github.com/dotnet/fsharp/issues/9928), [PR #19252](https://github.com/dotnet/fsharp/pull/19252))
diff --git a/src/Compiler/AbstractIL/ilsign.fs b/src/Compiler/AbstractIL/ilsign.fs
index e03f614244c..45f8239f1a9 100644
--- a/src/Compiler/AbstractIL/ilsign.fs
+++ b/src/Compiler/AbstractIL/ilsign.fs
@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
 
 module internal FSharp.Compiler.AbstractIL.StrongNameSign
 
@@ -301,19 +301,30 @@ let signStream stream keyBlob =
     patchSignature stream peReader signature
 
 let signatureSize (pk: byte array) =
-    if pk.Length < 25 then
-        raise (CryptographicException(getResourceString (FSComp.SR.ilSignInvalidPKBlob ())))
-
-    let mutable reader = BlobReader pk
-    reader.ReadBigInteger 12 |> ignore // Skip CLRHeader
-    reader.ReadBigInteger 8 |> ignore // Skip BlobHeader
-    let magic = reader.ReadInt32() // Read magic
-
-    if not (magic = RSA_PRIV_MAGIC || magic = RSA_PUB_MAGIC) then // RSAPubKey.magic
-        raise (CryptographicException(getResourceString (FSComp.SR.ilSignInvalidPKBlob ())))
-
-    let x = reader.ReadInt32() / 8
-    x
+    if isNull (box pk) || pk.Length < 16 then
+        0
+    else
+        let reader = BlobReader pk
+
+        let tryReadBitLen (offset: int) =
+            if pk.Length >= offset + 12 then
+                reader._offset <- offset
+                let magic = reader.ReadInt32()
+
+                if magic = RSA_PUB_MAGIC || magic = RSA_PRIV_MAGIC then
+                    let bitLen = reader.ReadInt32()
+                    Some bitLen
+                else
+                    None
+            else
+                None
+
+        match tryReadBitLen 8 with
+        | Some bitLen -> (bitLen / 8 + 7) &&& ~~~7
+        | None ->
+            match tryReadBitLen 20 with
+            | Some bitLen -> (bitLen / 8 + 7) &&& ~~~7
+            | None -> 128
 
 // Returns a CLR Format Blob public key
 let getPublicKeyForKeyPair keyBlob =