diff --git a/nix/overlays/by-name/pin-isabelle-2023/overlay.nix b/nix/overlays/by-name/pin-isabelle-2023/overlay.nix
new file mode 100644
index 00000000..6084bf40
--- /dev/null
+++ b/nix/overlays/by-name/pin-isabelle-2023/overlay.nix
@@ -0,0 +1,6 @@
+{sources}:
+#
+_: _: {
+  # Isabelle version 2023
+  isabelle-2023 = (import sources.pin-isabelle {}).isabelle;
+}
diff --git a/nix/overlays/top-level.nix b/nix/overlays/top-level.nix
index b8331e22..e7fa65ff 100644
--- a/nix/overlays/top-level.nix
+++ b/nix/overlays/top-level.nix
@@ -4,9 +4,6 @@ let
 in
   lib.composeManyExtensions [
     (final: _: {
-      # Isabelle version 2023
-      inherit (import sources.pin-isabelle {}) isabelle;
-
       # Wireshark bug
       # https://gitlab.com/wireshark/wireshark/-/issues/19574
       inherit (import sources.pin-wireshark {}) wireshark;