diff --git a/packaging/hydra.nix b/packaging/hydra.nix
index 664ee18caef..6df8782393d 100644
--- a/packaging/hydra.nix
+++ b/packaging/hydra.nix
@@ -187,6 +187,19 @@ in
           pkgs = nixpkgsFor.${system}.native;
         }
       );
+
+      nixpkgsLibTestsLazy = forAllSystems (
+        system:
+        lib.overrideDerivation
+          (import (nixpkgs + "/lib/tests/test-with-nix.nix") {
+            lib = nixpkgsFor.${system}.native.lib;
+            nix = self.packages.${system}.nix-cli;
+            pkgs = nixpkgsFor.${system}.native;
+          })
+          (_: {
+            "NIX_CONFIG" = "lazy-trees = true";
+          })
+      );
     };
 
   metrics.nixpkgs = import "${nixpkgs-regression}/pkgs/top-level/metrics.nix" {
diff --git a/src/nix-instantiate/nix-instantiate.cc b/src/nix-instantiate/nix-instantiate.cc
index 89a8505bb79..f327454ec91 100644
--- a/src/nix-instantiate/nix-instantiate.cc
+++ b/src/nix-instantiate/nix-instantiate.cc
@@ -17,6 +17,7 @@
 #include <map>
 #include <iostream>
 
+#include <nlohmann/json.hpp>
 
 using namespace nix;
 
@@ -58,12 +59,16 @@ void processExpr(EvalState & state, const Strings & attrPaths,
                         context);
                 // We intentionally don't output a newline here. The default PS1 for Bash in NixOS starts with a newline
                 // and other interactive shells like Zsh are smart enough to print a missing newline before the prompt.
-            else if (output == okXML)
-                printValueAsXML(state, strict, location, vRes, std::cout, context, noPos);
+            else if (output == okXML) {
+                std::ostringstream s;
+                printValueAsXML(state, strict, location, vRes, s, context, noPos);
+                std::cout << state.devirtualize(s.str(), context);
+            }
             else if (output == okJSON) {
-                printValueAsJSON(state, strict, vRes, v.determinePos(noPos), std::cout, context);
-                std::cout << std::endl;
-            } else {
+                auto j = printValueAsJSON(state, strict, vRes, v.determinePos(noPos), context);
+                std::cout << state.devirtualize(j.dump(), context) << std::endl;
+            }
+            else {
                 if (strict) state.forceValueDeep(vRes);
                 std::set<const void *> seen;
                 printAmbiguous(state, vRes, std::cout, &seen, std::numeric_limits<int>::max());