diff --git a/src/libstore/build-result.cc b/src/libstore/build-result.cc
index 3e316f679..e6469e38f 100644
--- a/src/libstore/build-result.cc
+++ b/src/libstore/build-result.cc
@@ -23,11 +23,20 @@ void to_json(nlohmann::json & json, const BuildResult & buildResult)
         json["stopTime"] = buildResult.stopTime;
 }
 
-nlohmann::json KeyedBuildResult::toJSON(Store & store) const
+void to_json(nlohmann::json & json, const KeyedBuildResult & buildResult)
 {
-    auto json = nlohmann::json((const BuildResult &) *this);
-    json["path"] = path.toJSON(store);
-    return json;
+    to_json(json, (const BuildResult &) buildResult);
+    auto path = nlohmann::json::object();
+    std::visit(
+        overloaded{
+            [&](const DerivedPathOpaque & opaque) { path["opaque"] = opaque.path.to_string(); },
+            [&](const DerivedPathBuilt & drv) {
+                path["drvPath"] = drv.drvPath->getBaseStorePath().to_string();
+                path["outputs"] = drv.outputs.to_string();
+            },
+        },
+        buildResult.path.raw());
+    json["path"] = std::move(path);
 }
 
 }
diff --git a/src/libstore/build-result.hh b/src/libstore/build-result.hh
index f56817f19..44862980d 100644
--- a/src/libstore/build-result.hh
+++ b/src/libstore/build-result.hh
@@ -134,10 +134,9 @@ struct KeyedBuildResult : BuildResult
     KeyedBuildResult(BuildResult res, DerivedPath path)
         : BuildResult(std::move(res)), path(std::move(path))
     { }
-
-    nlohmann::json toJSON(Store & store) const;
 };
 
 void to_json(nlohmann::json & json, const BuildResult & buildResult);
+void to_json(nlohmann::json & json, const KeyedBuildResult & buildResult);
 
 }
diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index 6c335e17c..a32dc5e53 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -1566,9 +1566,10 @@ Goal::Done DerivationGoal::done(
     logger->result(
         act ? act->id : getCurActivity(),
         resBuildResult,
-        KeyedBuildResult(
-            buildResult,
-            DerivedPath::Built{.drvPath = makeConstantStorePathRef(drvPath), .outputs = wantedOutputs}).toJSON(worker.store));
+        nlohmann::json(
+            KeyedBuildResult(
+                buildResult,
+                DerivedPath::Built{.drvPath = makeConstantStorePathRef(drvPath), .outputs = wantedOutputs})));
 
     return amDone(buildResult.success() ? ecSuccess : ecFailed, std::move(ex));
 }
diff --git a/src/libstore/build/substitution-goal.cc b/src/libstore/build/substitution-goal.cc
index 625e64781..41d8a0c30 100644
--- a/src/libstore/build/substitution-goal.cc
+++ b/src/libstore/build/substitution-goal.cc
@@ -42,9 +42,10 @@ Goal::Done PathSubstitutionGoal::done(
     logger->result(
         getCurActivity(),
         resBuildResult,
-        KeyedBuildResult(
-            buildResult,
-            DerivedPath::Opaque{storePath}).toJSON(worker.store));
+        nlohmann::json(
+            KeyedBuildResult(
+                buildResult,
+                DerivedPath::Opaque{storePath})));
 
     return amDone(result);
 }