diff --git a/flake.lock b/flake.lock
index e4bf8c71..377aed12 100644
--- a/flake.lock
+++ b/flake.lock
@@ -19,20 +19,19 @@
     "nix": {
       "inputs": {
         "lowdown-src": "lowdown-src",
-        "nixpkgs": "nixpkgs",
-        "nixpkgs-regression": "nixpkgs-regression"
+        "nixpkgs": "nixpkgs"
       },
       "locked": {
-        "lastModified": 1643066034,
-        "narHash": "sha256-xEPeMcNJVOeZtoN+d+aRwolpW8mFSEQx76HTRdlhPhg=",
+        "lastModified": 1639739069,
+        "narHash": "sha256-GOsiqy9EaTwDn2PLZ4eFj1VkXcBUbqrqHehRE9GuGdU=",
         "owner": "NixOS",
         "repo": "nix",
-        "rev": "a1cd7e58606a41fcf62bf8637804cf8306f17f62",
+        "rev": "b4f250417ab64f237c8b51439fe1f427193ab23b",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
-        "ref": "2.6.0",
+        "ref": "2.5.1",
         "repo": "nix",
         "type": "github"
       }
@@ -52,21 +51,6 @@
         "type": "indirect"
       }
     },
-    "nixpkgs-regression": {
-      "locked": {
-        "lastModified": 1643052045,
-        "narHash": "sha256-uGJ0VXIhWKGXxkeNnq4TvV3CIOkUJ3PAoLZ3HMzNVMw=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "215d4d0fd80ca5163643b03a33fde804a29cc1e2",
-        "type": "github"
-      },
-      "original": {
-        "id": "nixpkgs",
-        "rev": "215d4d0fd80ca5163643b03a33fde804a29cc1e2",
-        "type": "indirect"
-      }
-    },
     "root": {
       "inputs": {
         "nix": "nix",
diff --git a/flake.nix b/flake.nix
index d69048ed..188f2bf9 100644
--- a/flake.nix
+++ b/flake.nix
@@ -2,7 +2,7 @@
   description = "A Nix-based continuous build system";
 
   inputs.nixpkgs.follows = "nix/nixpkgs";
-  inputs.nix.url = github:NixOS/nix/2.6.0;
+  inputs.nix.url = "github:NixOS/nix/2.5.1";
 
   outputs = { self, nixpkgs, nix }:
     let
diff --git a/src/hydra-queue-runner/build-remote.cc b/src/hydra-queue-runner/build-remote.cc
index 69c82e72..464a35c8 100644
--- a/src/hydra-queue-runner/build-remote.cc
+++ b/src/hydra-queue-runner/build-remote.cc
@@ -287,9 +287,9 @@ void State::buildRemote(ref<Store> destStore,
            this will copy the inputs to the binary cache from the local
            store. */
         if (localStore != std::shared_ptr<Store>(destStore)) {
-            copyClosure(*localStore, *destStore,
-                step->drv->inputSrcs,
-                NoRepair, NoCheckSigs, NoSubstitute);
+            StorePathSet closure;
+            localStore->computeFSClosure(step->drv->inputSrcs, closure);
+            copyPaths(*localStore, *destStore, closure, NoRepair, NoCheckSigs, NoSubstitute);
         }
 
         {
diff --git a/src/hydra-queue-runner/queue-monitor.cc b/src/hydra-queue-runner/queue-monitor.cc
index 3f19d36a..49caf8e3 100644
--- a/src/hydra-queue-runner/queue-monitor.cc
+++ b/src/hydra-queue-runner/queue-monitor.cc
@@ -513,9 +513,9 @@ Step::ptr State::createStep(ref<Store> destStore,
                         // FIXME: should copy directly from substituter to destStore.
                     }
 
-                    copyClosure(*localStore, *destStore,
-                        StorePathSet { *path },
-                        NoRepair, CheckSigs, NoSubstitute);
+                    StorePathSet closure;
+                    localStore->computeFSClosure({*path}, closure);
+                    copyPaths(*localStore, *destStore, closure, NoRepair, CheckSigs, NoSubstitute);
 
                     time_t stopTime = time(0);