diff --git a/release.nix b/release.nix
index ce07010a..a3e2ffb5 100644
--- a/release.nix
+++ b/release.nix
@@ -1,5 +1,5 @@
 { hydraSrc ? builtins.fetchGit ./.
-, nixpkgs ? builtins.fetchGit { url = https://github.com/NixOS/nixpkgs-channels.git; ref = "nixos-19.09-small"; }
+, nixpkgs ? builtins.fetchTarball https://github.com/NixOS/nixpkgs/archive/release-19.09.tar.gz
 , officialRelease ? false
 , shell ? false
 }:
@@ -154,9 +154,7 @@ rec {
 
       preConfigure = "autoreconf -vfi";
 
-      NIX_LDFLAGS = [
-          "-lpthread"
-	];
+      NIX_LDFLAGS = [ "-lpthread" ];
 
       enableParallelBuilding = true;
 
diff --git a/src/hydra-eval-jobs/hydra-eval-jobs.cc b/src/hydra-eval-jobs/hydra-eval-jobs.cc
index 1514cf4b..deffaeae 100644
--- a/src/hydra-eval-jobs/hydra-eval-jobs.cc
+++ b/src/hydra-eval-jobs/hydra-eval-jobs.cc
@@ -109,7 +109,7 @@ static void worker(
         nlohmann::json reply;
 
         try {
-            auto v = findAlongAttrPath(state, attrPath, autoArgs, *vRoot).first;
+            auto v = findAlongAttrPath(state, attrPath, autoArgs, *vRoot);
 
             state.forceValue(*v);
 
@@ -138,23 +138,23 @@ static void worker(
 
                 /* If this is an aggregate, then get its constituents. */
                 auto a = v->attrs->get(state.symbols.create("_hydraAggregate"));
-                if (a && state.forceBool(*a->value, *a->pos)) {
+                if (a && state.forceBool(*(*a)->value, *(*a)->pos)) {
                     auto a = v->attrs->get(state.symbols.create("constituents"));
                     if (!a)
                         throw EvalError("derivation must have a ‘constituents’ attribute");
 
 
                     PathSet context;
-                    state.coerceToString(*a->pos, *a->value, context, true, false);
+                    state.coerceToString(*(*a)->pos, *(*a)->value, context, true, false);
                     for (auto & i : context)
                         if (i.at(0) == '!') {
                             size_t index = i.find("!", 1);
                             job["constituents"].push_back(string(i, index + 1));
                         }
 
-                    state.forceList(*a->value, *a->pos);
-                    for (unsigned int n = 0; n < a->value->listSize(); ++n) {
-                        auto v = a->value->listElems()[n];
+                    state.forceList(*(*a)->value, *(*a)->pos);
+                    for (unsigned int n = 0; n < (*a)->value->listSize(); ++n) {
+                        auto v = (*a)->value->listElems()[n];
                         state.forceValue(*v);
                         if (v->type == tString)
                             job["namedConstituents"].push_back(state.forceStringNoCtx(*v));