diff --git a/common.nix b/common.nix
index 46a3010..9affa2b 100644
--- a/common.nix
+++ b/common.nix
@@ -101,6 +101,8 @@
 
     coq_8_5
     emacsPackages.proofgeneral_4_3_pre
+
+    stablePkgs # protect nixpkgs checkout from GC
   ] ++ (with aspellDicts; [ en de fr nl ]);
 
   nixpkgs.config.packageOverrides = pkgs: with pkgs; let
@@ -110,10 +112,10 @@
       owner = "NixOS";
       repo = "nixpkgs-channels";
     };
-    stable = import (fetchNixPkgs {
+    stablePkgs = fetchNixPkgs {
       rev = "f231b2b3f79020025eaabe4e8fae53e81651914c";
       sha256 = "0bnac2qsx2j5gl2vfqjswv096fnqvf7d5ids1442mk050yph0gix";
-    }) {};
+    };
   in {
     idea.idea-community = pkgs.idea.idea-community.overrideDerivation (oldAttrs: rec {
         name = "idea-community-${version}";
@@ -128,7 +130,8 @@
       extraPythonPackages = [ pkgs.pythonPackages.websocket_client ];
     };
 
-    stable = stable;
+    stablePkgs = stablePkgs;
+    stable = import stablePkgs {};
   };
 
   nixpkgs.config.allowTexliveBuilds = true;