diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index 9f1271ea7..a4e04e78a 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -1228,13 +1228,13 @@ DerivationOutput DerivationOutput::fromJSON(
         keys.insert(key);
 
     auto methodAlgo = [&]() -> std::pair<ContentAddressMethod, HashAlgorithm> {
-        auto & method_ = getString(valueAt(json, "method"));
-        ContentAddressMethod method = ContentAddressMethod::parse(method_);
+        ContentAddressMethod method = ContentAddressMethod::parse(
+            getString(valueAt(json, "method")));
         if (method == ContentAddressMethod::Raw::Text)
             xpSettings.require(Xp::DynamicDerivations);
 
-        auto & hashAlgo_ = getString(valueAt(json, "hashAlgo"));
-        auto hashAlgo = parseHashAlgo(hashAlgo_);
+        auto hashAlgo = parseHashAlgo(
+            getString(valueAt(json, "hashAlgo")));
         return { std::move(method), std::move(hashAlgo) };
     };
 
@@ -1351,7 +1351,8 @@ Derivation Derivation::fromJSON(
     res.name = getString(valueAt(json, "name"));
 
     try {
-        for (auto & [outputName, output] : getObject(valueAt(json, "outputs"))) {
+        auto outputs = getObject(valueAt(json, "outputs"));
+        for (auto & [outputName, output] : outputs) {
             res.outputs.insert_or_assign(
                 outputName,
                 DerivationOutput::fromJSON(store, res.name, outputName, output));
@@ -1362,7 +1363,8 @@ Derivation Derivation::fromJSON(
     }
 
     try {
-        for (auto & input : getArray(valueAt(json, "inputSrcs")))
+        auto inputSrcs = getArray(valueAt(json, "inputSrcs"));
+        for (auto & input : inputSrcs)
             res.inputSrcs.insert(store.parseStorePath(static_cast<const std::string &>(input)));
     } catch (Error & e) {
         e.addTrace({}, "while reading key 'inputSrcs'");
@@ -1375,13 +1377,15 @@ Derivation Derivation::fromJSON(
             auto & json = getObject(_json);
             DerivedPathMap<StringSet>::ChildNode node;
             node.value = getStringSet(valueAt(json, "outputs"));
-            for (auto & [outputId, childNode] : getObject(valueAt(json, "dynamicOutputs"))) {
+            auto drvs = getObject(valueAt(json, "dynamicOutputs"));
+            for (auto & [outputId, childNode] : drvs) {
                 xpSettings.require(Xp::DynamicDerivations);
                 node.childMap[outputId] = doInput(childNode);
             }
             return node;
         };
-        for (auto & [inputDrvPath, inputOutputs] : getObject(valueAt(json, "inputDrvs")))
+        auto drvs = getObject(valueAt(json, "inputDrvs"));
+        for (auto & [inputDrvPath, inputOutputs] : drvs)
             res.inputDrvs.map[store.parseStorePath(inputDrvPath)] =
                 doInput(inputOutputs);
     } catch (Error & e) {
diff --git a/src/libutil-tests/json-utils.cc b/src/libutil-tests/json-utils.cc
index 051d86ec7..00b8646f1 100644
--- a/src/libutil-tests/json-utils.cc
+++ b/src/libutil-tests/json-utils.cc
@@ -63,9 +63,7 @@ TEST(valueAt, simpleObject) {
 
     auto nested = R"({ "hello": { "world": "" } })"_json;
 
-    auto & nestedObject = valueAt(getObject(nested), "hello");
-
-    ASSERT_EQ(valueAt(nestedObject, "world"), "");
+    ASSERT_EQ(valueAt(valueAt(getObject(nested), "hello"), "world"), "");
 }
 
 TEST(valueAt, missingKey) {
@@ -83,7 +81,7 @@ TEST(getObject, rightAssertions) {
 
     auto nested = R"({ "object": { "object": {} } })"_json;
 
-    auto & nestedObject = getObject(valueAt(getObject(nested), "object"));
+    auto nestedObject = getObject(valueAt(getObject(nested), "object"));
 
     ASSERT_EQ(nestedObject, getObject(nlohmann::json::parse(R"({ "object": {} })")));
     ASSERT_EQ(getObject(valueAt(getObject(nestedObject), "object")), (nlohmann::json::object_t {}));