diff --git a/nix/overlays/pin-isabelle-2023.nix b/nix/overlays/pin-isabelle-2023.nix
deleted file mode 100644
index c5cbab6f..00000000
--- a/nix/overlays/pin-isabelle-2023.nix
+++ /dev/null
@@ -1,7 +0,0 @@
-let
-  sources = import ../../npins;
-in
-_: _: {
-  # Isabelle version 2023
-  isabelle-2023 = (import sources.pin-isabelle { }).isabelle;
-}