diff --git a/biosimdb_interface/form/utils.py b/biosimdb_interface/form/utils.py
index f77ea72..0a54e8d 100644
--- a/biosimdb_interface/form/utils.py
+++ b/biosimdb_interface/form/utils.py
@@ -165,12 +165,12 @@ def form_to_json(form):
                     value = bool(value)
             converted_values.append(value)
 
-        # For repeated keys keep list (after dropping empty placeholders);
-        # for single keys keep scalar to preserve existing behavior.
-        if len(converted_values) > 1:
-            value_out = [v for v in converted_values if v != ""]
-        else:
-            value_out = converted_values[0] if converted_values else ""
+            # HTML names ending in [] represent schema multivalued fields, even when
+            # the user selects only one option.
+            if key.endswith("[]"):
+                value_out = [value for value in converted_values if value != ""]
+            else:
+                value_out = converted_values[0] if converted_values else ""
 
         _set_nested(data, parts, value_out)
     return data
diff --git a/biosimdb_interface/form/webform.py b/biosimdb_interface/form/webform.py
index 773d0a7..6c461ed 100644
--- a/biosimdb_interface/form/webform.py
+++ b/biosimdb_interface/form/webform.py
@@ -117,7 +117,7 @@ def webform():
 
             if action == "save":
                 json_form["files"] = extract_uploaded_file_metadata(tmpdir)
-
+            print(json_form)
             biosimschema_path = os.getenv("BIOSIM_SCHEMA_PATH", "")
 
             validation_errors = []
diff --git a/tests/test_form/test_utils.py b/tests/test_form/test_utils.py
index 8068292..df75e2d 100644
--- a/tests/test_form/test_utils.py
+++ b/tests/test_form/test_utils.py
@@ -63,3 +63,14 @@ def test_form_to_json_direct_list_assignment():
     d = {}
     _set_nested(d, ["items", "1"], "val")
     assert d == {"items": ["val"]}
+
+
+def test_form_to_json_multiselect_single_value_stays_list():
+    """A single selection from a multivalued HTML field remains a list."""
+    result = form_to_json(
+        {"stages[minimisation][1][minimisation_algorithm][]": "Steepest Descent"}
+    )
+
+    assert result == {
+        "stages": {"minimisation": [{"minimisation_algorithm": ["Steepest Descent"]}]}
+    }