diff --git a/src/spikeinterface/curation/curation_format.py b/src/spikeinterface/curation/curation_format.py
index babe7aac40..511abb7801 100644
--- a/src/spikeinterface/curation/curation_format.py
+++ b/src/spikeinterface/curation/curation_format.py
@@ -92,13 +92,17 @@ def convert_from_sortingview_curation_format_v0(sortingview_dict, destination_fo
     """
 
     assert destination_format == "1"
-
+    if "mergeGroups" not in sortingview_dict.keys():
+        sortingview_dict["mergeGroups"] = []
     merge_groups = sortingview_dict["mergeGroups"]
     merged_units = sum(merge_groups, [])
-    if len(merged_units) > 0:
-        unit_id_type = int if isinstance(merged_units[0], int) else str
+
+    first_unit_id = next(iter(sortingview_dict["labelsByUnit"].keys()))
+    if str.isdigit(first_unit_id):
+        unit_id_type = int
     else:
         unit_id_type = str
+
     all_units = []
     all_labels = []
     manual_labels = []
diff --git a/src/spikeinterface/curation/tests/sv-sorting-curation-no-merge.json b/src/spikeinterface/curation/tests/sv-sorting-curation-no-merge.json
new file mode 100644
index 0000000000..2a350340f3
--- /dev/null
+++ b/src/spikeinterface/curation/tests/sv-sorting-curation-no-merge.json
@@ -0,0 +1 @@
+{"labelsByUnit":{"2":["mua"],"3":["mua"],"4":["mua"],"5":["accept"],"6":["accept"],"7":["accept"],"8":["artifact"],"9":["artifact"]}}
diff --git a/src/spikeinterface/curation/tests/test_sortingview_curation.py b/src/spikeinterface/curation/tests/test_sortingview_curation.py
index bb152e7f71..945aca7937 100644
--- a/src/spikeinterface/curation/tests/test_sortingview_curation.py
+++ b/src/spikeinterface/curation/tests/test_sortingview_curation.py
@@ -243,11 +243,23 @@ def test_label_inheritance_str():
     assert np.all(sorting_include_accept.get_property("accept"))
 
 
+def test_json_no_merge_curation():
+    """
+    Test curation with no merges using a JSON file.
+    """
+    sorting = generate_sorting(num_units=10)
+
+    json_file = parent_folder / "sv-sorting-curation-no-merge.json"
+    sorting_curated = apply_sortingview_curation(sorting, uri_or_json=json_file)
+
+
 if __name__ == "__main__":
     # generate_sortingview_curation_dataset()
     # test_sha1_curation()
+
     test_gh_curation()
     test_json_curation()
     test_false_positive_curation()
     test_label_inheritance_int()
     test_label_inheritance_str()
+    test_json_no_merge_curation()