diff --git a/tests/infrastructure/xlsx/test_scenario_export_workbook.py b/tests/infrastructure/xlsx/test_scenario_export_workbook.py
index d1dfaa79c..4bf13859e 100644
--- a/tests/infrastructure/xlsx/test_scenario_export_workbook.py
+++ b/tests/infrastructure/xlsx/test_scenario_export_workbook.py
@@ -28,3 +28,23 @@ def test_renders_a_sheet_named_for_the_scenario_with_headers_then_rows() -> None
     worksheet = workbook["Fabric first"]
     assert [cell.value for cell in worksheet[1]] == ["property_id", "loft_insulation"]
     assert [cell.value for cell in worksheet[2]] == [1, 1200.0]
+
+
+def test_sanitises_and_deduplicates_scenario_sheet_names() -> None:
+    # arrange — a name over Excel's 31-char limit (used twice, so it must be
+    # deduplicated) and one with characters Excel forbids in a sheet title.
+    empty = ExportSheet(columns=("property_id",), rows=())
+    long_name = "A really long scenario name that exceeds Excel's limit"
+    illegal_name = "Bad:/\\?*[]name"
+
+    # act
+    data = render_workbook(
+        [(long_name, empty), (long_name, empty), (illegal_name, empty)]
+    )
+
+    # assert — three distinct, Excel-legal sheet names.
+    names = load_workbook(BytesIO(data)).sheetnames
+    assert len(names) == 3
+    assert len(set(names)) == 3
+    assert all(len(name) <= 31 for name in names)
+    assert not any(ch in name for name in names for ch in r":/\?*[]")