diff --git a/default.nix b/default.nix
index abfcda4..b052317 100644
--- a/default.nix
+++ b/default.nix
@@ -1,6 +1,6 @@
 { stdenv
 , lib
-, nixFlakes
+, nixUnstable
 , meson
 , cmake
 , ninja
@@ -21,7 +21,7 @@ stdenv.mkDerivation rec {
   src = if srcDir == null then filterMesonBuild ./. else srcDir;
   buildInputs = [
     nlohmann_json
-    nixFlakes
+    nixUnstable
     boost
   ];
   nativeBuildInputs = [
diff --git a/flake.lock b/flake.lock
index ea8caf8..6063da8 100644
--- a/flake.lock
+++ b/flake.lock
@@ -17,11 +17,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1637048323,
-        "narHash": "sha256-h2m2LuUEbV5pvNjXoWbk2rAaBAQAsf3cvJXS8DGi+Bo=",
+        "lastModified": 1639573498,
+        "narHash": "sha256-YAoywqjyjOJYuEZpA8sln84jk99GG9hYbPEYXwGEGGM=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "6b68d74f036def3d48a23969edfd0fa47f34af3e",
+        "rev": "aef12c8678fd5e927edba764bd04f3ba2930ae15",
         "type": "github"
       },
       "original": {
diff --git a/src/nix-eval-jobs.cc b/src/nix-eval-jobs.cc
index c07ca9b..b6614b0 100644
--- a/src/nix-eval-jobs.cc
+++ b/src/nix-eval-jobs.cc
@@ -188,7 +188,7 @@ static void worker(
                     continue;
                   }
 
-                  printValueAsJSON(state, true, *metaValue, ss, context);
+                  printValueAsJSON(state, true, *metaValue, noPos, ss, context);
                   nlohmann::json field = nlohmann::json::parse(ss.str());
                   meta[name] = field;
                 }