diff --git a/pkgs/overlays/unstable-from-source.nix b/pkgs/overlays/unstable-from-source.nix
index 4b40bcb..416b778 100644
--- a/pkgs/overlays/unstable-from-source.nix
+++ b/pkgs/overlays/unstable-from-source.nix
@@ -32,9 +32,9 @@ let
     # config -> pkgs.config
     config = self.config;
     # overlays -> pkgs.buildPackages.overlays
-    overlays = overlays.allLayers;
+    overlays = overlays.allLayers or [];
     # crossOverlays -> pkgs.overlays without pkgs.buildPackages.overlays
-    crossOverlays = overlays.finalLayer;
+    crossOverlays = overlays.finalLayer or [];
   } // self.lib.optionalAttrs (
     self.lib.systems.equals self.stdenv.buildPlatform self.stdenv.hostPlatform
   ) {