diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index 3978cc63611..0adff8c46e3 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -1392,8 +1392,7 @@ Derivation Derivation::fromJSON(
         std::function<DerivedPathMap<StringSet>::ChildNode(const nlohmann::json &)> doInput;
         doInput = [&](const auto & json) {
             DerivedPathMap<StringSet>::ChildNode node;
-            node.value = static_cast<const StringSet &>(
-                ensureType(valueAt(json, "outputs"), value_t::array));
+            node.value = getStringSet(valueAt(json, "outputs"));
             for (auto & [outputId, childNode] : getObject(valueAt(json, "dynamicOutputs"))) {
                 xpSettings.require(Xp::DynamicDerivations);
                 node.childMap[outputId] = doInput(childNode);
@@ -1411,8 +1410,8 @@ Derivation Derivation::fromJSON(
 
     res.platform = getString(valueAt(json, "system"));
     res.builder = getString(valueAt(json, "builder"));
-    res.args = ensureType(valueAt(json, "args"), value_t::array);
-    res.env = ensureType(valueAt(json, "env"), value_t::object);
+    res.args = getStringList(valueAt(json, "args"));
+    res.env = getStringMap(valueAt(json, "env"));
 
     return res;
 }
diff --git a/src/libutil/json-utils.cc b/src/libutil/json-utils.cc
index 9df2543d21f..e2260199a2e 100644
--- a/src/libutil/json-utils.cc
+++ b/src/libutil/json-utils.cc
@@ -90,4 +90,36 @@ const nlohmann::json::boolean_t & getBoolean(const nlohmann::json & value)
 
     return value.get_ref<const nlohmann::json::boolean_t &>();
 }
+
+StringSet getStringSet(const nlohmann::json & value)
+{
+    StringSet stringSet = {};
+    auto asArray = getArray(value);
+    for(auto & elem: asArray){
+        stringSet.insert(getString(elem));
+    }
+    return stringSet;
+}
+
+Strings getStringList(const nlohmann::json & value)
+{
+    Strings stringList = {};
+    auto asArray = getArray(value);
+    for(auto & elem: asArray){
+        stringList.push_back(getString(elem));
+    }
+    return stringList;
+}
+
+
+StringMap getStringMap(const nlohmann::json & value)
+{
+    StringMap stringMap = {};
+    auto asObject = getObject(value);
+    for(auto & [key, elem]: asObject){
+        stringMap.insert(key, getString(elem));
+    }
+    return stringMap;
+}
+
 }
diff --git a/src/libutil/json-utils.hh b/src/libutil/json-utils.hh
index 6b75516f907..91d7faff0d8 100644
--- a/src/libutil/json-utils.hh
+++ b/src/libutil/json-utils.hh
@@ -3,6 +3,7 @@
 
 #include <nlohmann/json.hpp>
 #include <list>
+#include "types.hh"
 
 namespace nix {
 
@@ -41,6 +42,9 @@ const nlohmann::json::array_t & getArray(const nlohmann::json & value);
 const nlohmann::json::string_t & getString(const nlohmann::json & value);
 const nlohmann::json::number_integer_t & getInteger(const nlohmann::json & value);
 const nlohmann::json::boolean_t & getBoolean(const nlohmann::json & value);
+StringSet getStringSet(const nlohmann::json & value);
+Strings getStringList(const nlohmann::json & value);
+StringMap getStringMap(const nlohmann::json & value);
 
 /**
  * For `adl_serializer<std::optional<T>>` below, we need to track what