diff --git a/lix/libcmd/built-path.cc b/lix/libcmd/built-path.cc
index e05b16ae2..703396925 100644
--- a/lix/libcmd/built-path.cc
+++ b/lix/libcmd/built-path.cc
@@ -80,38 +80,47 @@ SingleDerivedPath SingleBuiltPath::discardOutputPath() const
     );
 }
 
-nlohmann::json BuiltPath::Built::toJSON(const Store & store) const
-{
+kj::Promise<Result<nlohmann::json>> BuiltPath::Built::toJSON(const Store & store) const
+try {
     nlohmann::json res;
-    res["drvPath"] = drvPath->toJSON(store);
+    res["drvPath"] = TRY_AWAIT(drvPath->toJSON(store));
     for (const auto & [outputName, outputPath] : outputs) {
         res["outputs"][outputName] = store.printStorePath(outputPath);
     }
-    return res;
+    co_return res;
+} catch (...) {
+    co_return result::current_exception();
 }
 
-nlohmann::json SingleBuiltPath::Built::toJSON(const Store & store) const
-{
+kj::Promise<Result<nlohmann::json>> SingleBuiltPath::Built::toJSON(const Store & store) const
+try {
     nlohmann::json res;
-    res["drvPath"] = drvPath->toJSON(store);
+    res["drvPath"] = TRY_AWAIT(drvPath->toJSON(store));
     auto & [outputName, outputPath] = output;
     res["output"] = outputName;
     res["outputPath"] = store.printStorePath(outputPath);
-    return res;
+    co_return res;
+} catch (...) {
+    co_return result::current_exception();
 }
 
-nlohmann::json SingleBuiltPath::toJSON(const Store & store) const
-{
-    return std::visit([&](const auto & buildable) {
+kj::Promise<Result<nlohmann::json>> SingleBuiltPath::toJSON(const Store & store) const
+try {
+    co_return TRY_AWAIT(std::visit([&](const auto & buildable) {
         return buildable.toJSON(store);
-    }, raw());
+    }, raw()));
+} catch (...) {
+    co_return result::current_exception();
 }
 
-nlohmann::json BuiltPath::toJSON(const Store & store) const
-{
-    return std::visit([&](const auto & buildable) {
+
+kj::Promise<Result<nlohmann::json>> BuiltPath::toJSON(const Store & store) const
+try {
+    co_return TRY_AWAIT(std::visit([&](const auto & buildable) {
         return buildable.toJSON(store);
-    }, raw());
+    }, raw()));
+} catch (...) {
+    co_return result::current_exception();
 }
 
 kj::Promise<Result<RealisedPath::Set>> BuiltPath::toRealisedPaths(Store & store) const
diff --git a/lix/libcmd/built-path.hh b/lix/libcmd/built-path.hh
index e3c015c00..0ddf0f5e7 100644
--- a/lix/libcmd/built-path.hh
+++ b/lix/libcmd/built-path.hh
@@ -17,7 +17,7 @@ struct SingleBuiltPathBuilt {
 
     std::string to_string(const Store & store) const;
     static SingleBuiltPathBuilt parse(const Store & store, std::string_view, std::string_view);
-    nlohmann::json toJSON(const Store & store) const;
+    kj::Promise<Result<nlohmann::json>> toJSON(const Store & store) const;
 
     DECLARE_CMP(SingleBuiltPathBuilt);
 };
@@ -45,7 +45,7 @@ struct SingleBuiltPath : built_path::detail::SingleBuiltPathRaw {
     SingleDerivedPath discardOutputPath() const;
 
     static SingleBuiltPath parse(const Store & store, std::string_view);
-    nlohmann::json toJSON(const Store & store) const;
+    kj::Promise<Result<nlohmann::json>> toJSON(const Store & store) const;
 };
 
 static inline ref<SingleBuiltPath> staticDrv(StorePath drvPath)
@@ -64,7 +64,7 @@ struct BuiltPathBuilt {
 
     std::string to_string(const Store & store) const;
     static BuiltPathBuilt parse(const Store & store, std::string_view, std::string_view);
-    nlohmann::json toJSON(const Store & store) const;
+    kj::Promise<Result<nlohmann::json>> toJSON(const Store & store) const;
 
     DECLARE_CMP(BuiltPathBuilt);
 };
@@ -94,7 +94,7 @@ struct BuiltPath : built_path::detail::BuiltPathRaw {
     StorePathSet outPaths() const;
     kj::Promise<Result<RealisedPath::Set>> toRealisedPaths(Store & store) const;
 
-    nlohmann::json toJSON(const Store & store) const;
+    kj::Promise<Result<nlohmann::json>> toJSON(const Store & store) const;
 };
 
 typedef std::vector<BuiltPath> BuiltPaths;
diff --git a/lix/libstore/derived-path.cc b/lix/libstore/derived-path.cc
index f042f234b..592938e40 100644
--- a/lix/libstore/derived-path.cc
+++ b/lix/libstore/derived-path.cc
@@ -28,14 +28,17 @@ CMP(SingleDerivedPath, DerivedPathBuilt, outputs)
 #undef CMP
 #undef CMP_ONE
 
-nlohmann::json DerivedPath::Opaque::toJSON(const Store & store) const
-{
-    return store.printStorePath(path);
+kj::Promise<Result<nlohmann::json>> DerivedPath::Opaque::toJSON(const Store & store) const
+try {
+    return {store.printStorePath(path)};
+} catch (...) {
+    return {result::current_exception()};
 }
 
-nlohmann::json SingleDerivedPath::Built::toJSON(Store & store) const {
+kj::Promise<Result<nlohmann::json>> SingleDerivedPath::Built::toJSON(Store & store) const
+try {
     nlohmann::json res;
-    res["drvPath"] = drvPath->toJSON(store);
+    res["drvPath"] = TRY_AWAIT(drvPath->toJSON(store));
     // Fallback for the input-addressed derivation case: We expect to always be
     // able to print the output paths, so let’s do it
     // FIXME try-resolve on drvPath
@@ -48,12 +51,15 @@ nlohmann::json SingleDerivedPath::Built::toJSON(Store & store) const {
         res["outputPath"] = store.printStorePath(*p);
     else
         res["outputPath"] = nullptr;
-    return res;
+    co_return res;
+} catch (...) {
+    co_return result::current_exception();
 }
 
-nlohmann::json DerivedPath::Built::toJSON(Store & store) const {
+kj::Promise<Result<nlohmann::json>> DerivedPath::Built::toJSON(Store & store) const
+try {
     nlohmann::json res;
-    res["drvPath"] = drvPath->toJSON(store);
+    res["drvPath"] = TRY_AWAIT(drvPath->toJSON(store));
     // Fallback for the input-addressed derivation case: We expect to always be
     // able to print the output paths, so let’s do it
     // FIXME try-resolve on drvPath
@@ -65,21 +71,27 @@ nlohmann::json DerivedPath::Built::toJSON(Store & store) const {
         else
             res["outputs"][output] = nullptr;
     }
-    return res;
+    co_return res;
+} catch (...) {
+    co_return result::current_exception();
 }
 
-nlohmann::json SingleDerivedPath::toJSON(Store & store) const
-{
-    return std::visit([&](const auto & buildable) {
+kj::Promise<Result<nlohmann::json>> SingleDerivedPath::toJSON(Store & store) const
+try {
+    co_return TRY_AWAIT(std::visit([&](const auto & buildable) {
         return buildable.toJSON(store);
-    }, raw());
+    }, raw()));
+} catch (...) {
+    co_return result::current_exception();
 }
 
-nlohmann::json DerivedPath::toJSON(Store & store) const
-{
-    return std::visit([&](const auto & buildable) {
+kj::Promise<Result<nlohmann::json>> DerivedPath::toJSON(Store & store) const
+try {
+    co_return TRY_AWAIT(std::visit([&](const auto & buildable) {
         return buildable.toJSON(store);
-    }, raw());
+    }, raw()));
+} catch (...) {
+    co_return result::current_exception();
 }
 
 std::string DerivedPath::Opaque::to_string(const Store & store) const
diff --git a/lix/libstore/derived-path.hh b/lix/libstore/derived-path.hh
index d110ce434..e9994f181 100644
--- a/lix/libstore/derived-path.hh
+++ b/lix/libstore/derived-path.hh
@@ -6,7 +6,9 @@
 #include "lix/libstore/outputs-spec.hh"
 #include "lix/libutil/comparator.hh"
 #include "lix/libutil/ref.hh"
+#include "lix/libutil/result.hh"
 
+#include <kj/async.h>
 #include <variant>
 
 #include <nlohmann/json_fwd.hpp>
@@ -27,7 +29,7 @@ struct DerivedPathOpaque {
 
     std::string to_string(const Store & store) const;
     static DerivedPathOpaque parse(const Store & store, std::string_view);
-    nlohmann::json toJSON(const Store & store) const;
+    kj::Promise<Result<nlohmann::json>> toJSON(const Store & store) const;
 
     GENERATE_CMP(DerivedPathOpaque, me->path);
 };
@@ -74,7 +76,7 @@ struct SingleDerivedPathBuilt {
         const Store & store, ref<SingleDerivedPath> drvPath,
         OutputNameView outputs,
         const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
-    nlohmann::json toJSON(Store & store) const;
+    kj::Promise<Result<nlohmann::json>> toJSON(Store & store) const;
 
     DECLARE_CMP(SingleDerivedPathBuilt);
 };
@@ -146,7 +148,7 @@ struct SingleDerivedPath : derived_path::detail::SingleDerivedPathRaw {
         const Store & store,
         std::string_view,
         const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
-    nlohmann::json toJSON(Store & store) const;
+    kj::Promise<Result<nlohmann::json>> toJSON(Store & store) const;
 };
 
 static inline ref<SingleDerivedPath> makeConstantStorePathRef(StorePath drvPath)
@@ -199,7 +201,7 @@ struct DerivedPathBuilt {
         const Store & store, ref<SingleDerivedPath>,
         std::string_view,
         const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
-    nlohmann::json toJSON(Store & store) const;
+    kj::Promise<Result<nlohmann::json>> toJSON(Store & store) const;
 
     DECLARE_CMP(DerivedPathBuilt);
 };
@@ -276,7 +278,7 @@ struct DerivedPath : derived_path::detail::DerivedPathRaw {
      */
     static DerivedPath fromSingle(const SingleDerivedPath &);
 
-    nlohmann::json toJSON(Store & store) const;
+    kj::Promise<Result<nlohmann::json>> toJSON(Store & store) const;
 };
 
 typedef std::vector<DerivedPath> DerivedPaths;
diff --git a/lix/nix/build.cc b/lix/nix/build.cc
index 7602f719f..432698fba 100644
--- a/lix/nix/build.cc
+++ b/lix/nix/build.cc
@@ -9,23 +9,25 @@
 
 using namespace nix;
 
-static nlohmann::json derivedPathsToJSON(const DerivedPaths & paths, Store & store)
+static nlohmann::json derivedPathsToJSON(AsyncIoRoot & aio, const DerivedPaths & paths, Store & store)
 {
     auto res = nlohmann::json::array();
     for (auto & t : paths) {
         std::visit([&](const auto & t) {
-            res.push_back(t.toJSON(store));
+            res.push_back(aio.blockOn(t.toJSON(store)));
         }, t.raw());
     }
     return res;
 }
 
-static nlohmann::json builtPathsWithResultToJSON(const std::vector<BuiltPathWithResult> & buildables, const Store & store)
+static nlohmann::json builtPathsWithResultToJSON(
+    AsyncIoRoot & aio, const std::vector<BuiltPathWithResult> & buildables, const Store & store
+)
 {
     auto res = nlohmann::json::array();
     for (auto & b : buildables) {
         std::visit([&](const auto & t) {
-            auto j = t.toJSON(store);
+            auto j = aio.blockOn(t.toJSON(store));
             if (b.result) {
                 if (b.result->startTime)
                     j["startTime"] = b.result->startTime;
@@ -132,7 +134,7 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
             printMissing(store, pathsToBuild, lvlError);
 
             if (json)
-                logger->cout("%s", derivedPathsToJSON(pathsToBuild, *store).dump());
+                logger->cout("%s", derivedPathsToJSON(aio(), pathsToBuild, *store).dump());
 
             return;
         }
@@ -143,7 +145,7 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
             installables,
             repair ? bmRepair : buildMode);
 
-        if (json) logger->cout("%s", builtPathsWithResultToJSON(buildables, *store).dump());
+        if (json) logger->cout("%s", builtPathsWithResultToJSON(aio(), buildables, *store).dump());
 
         if (outLink != "")
             if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())