diff --git a/src/zarr.v3.cpp b/src/zarr.v3.cpp
index d3c060e5..7237147d 100644
--- a/src/zarr.v3.cpp
+++ b/src/zarr.v3.cpp
@@ -302,7 +302,9 @@ zarr::ZarrV3::write_group_metadata_() const
     using json = nlohmann::json;
 
     json metadata;
-    metadata["attributes"]["acquire"] = json::parse(external_metadata_json_);
+    metadata["attributes"]["acquire"] =
+      external_metadata_json_.empty() ? ""
+                                      : json::parse(external_metadata_json_);
 
     auto path = (dataset_root_ / "meta" / "root.group.json").string();
     common::write_string(path, metadata.dump(4));
diff --git a/tests/write-zarr-v3-raw.cpp b/tests/write-zarr-v3-raw.cpp
index b70637a7..047bca80 100644
--- a/tests/write-zarr-v3-raw.cpp
+++ b/tests/write-zarr-v3-raw.cpp
@@ -98,15 +98,14 @@ setup(AcquireRuntime* runtime)
                                 SIZED("ZarrV3"),
                                 &props.video[0].storage.identifier));
 
-    const char external_metadata[] = R"({"hello":"world"})";
     const struct PixelScale sample_spacing_um = { 1, 1 };
 
     storage_properties_init(&props.video[0].storage.settings,
                             0,
                             (char*)filename,
                             strlen(filename) + 1,
-                            (char*)external_metadata,
-                            sizeof(external_metadata),
+                            nullptr,
+                            0,
                             sample_spacing_um);
 
     storage_properties_set_chunking_props(&props.video[0].storage.settings,
@@ -217,7 +216,7 @@ validate(AcquireRuntime* runtime)
 
     f = std::ifstream(metadata_path);
     metadata = json::parse(f);
-    CHECK("world" == metadata["attributes"]["acquire"]["hello"]);
+    CHECK("" == metadata["attributes"]["acquire"]);
 
     // check the array metadata file
     metadata_path = test_path / "meta" / "root" / "0.array.json";