diff --git a/src/backend/api/routers/measurements.py b/src/backend/api/routers/measurements.py
index bb466d9..cc264e1 100644
--- a/src/backend/api/routers/measurements.py
+++ b/src/backend/api/routers/measurements.py
@@ -359,8 +359,11 @@ async def export_measurements_csv(
         # Format decimals with configured separator
         # #118: quota non misurata dalla visione -> NaN
         value_str = "NaN" if m.value is None else str(m.value).replace(".", decimal_separator)
+        # #124: quota NaN (value None) -> deviazione NaN, non vuota
         deviation_str = (
-            str(m.deviation).replace(".", decimal_separator)
+            "NaN"
+            if m.value is None
+            else str(m.deviation).replace(".", decimal_separator)
             if m.deviation is not None
             else ""
         )
diff --git a/src/backend/services/production_export_service.py b/src/backend/services/production_export_service.py
index c547f87..5298984 100644
--- a/src/backend/services/production_export_service.py
+++ b/src/backend/services/production_export_service.py
@@ -160,7 +160,7 @@ async def build_statistics_csv(db: AsyncSession, run: ProductionRun) -> str:
             neutralise_csv_cell(subtask.description) if subtask else "",
             number(subtask.nominal) if subtask else "",
             number(measurement.value) if measurement.value is not None else "NaN",  # #118
-            number(measurement.deviation),
+            "NaN" if measurement.value is None else number(measurement.deviation),  # #124: quota NaN -> deviazione NaN
             measurement.pass_fail,
             number(subtask.ltl) if subtask else "",
             number(subtask.lwl) if subtask else "",
diff --git a/src/backend/tests/test_nan_measurements.py b/src/backend/tests/test_nan_measurements.py
index a0d43be..583f3f7 100644
--- a/src/backend/tests/test_nan_measurements.py
+++ b/src/backend/tests/test_nan_measurements.py
@@ -111,4 +111,4 @@ async def test_csv_export_writes_nan(
     row = by_id[str(nan.id)]
     assert row[header.index("value")] == "NaN"
     assert row[header.index("pass_fail")] == "fail"
-    assert row[header.index("deviation")] == ""
+    assert row[header.index("deviation")] == "NaN"  # #124
diff --git a/src/backend/tests/test_production_runs.py b/src/backend/tests/test_production_runs.py
index c76c326..c4b196a 100644
--- a/src/backend/tests/test_production_runs.py
+++ b/src/backend/tests/test_production_runs.py
@@ -836,3 +836,31 @@ async def test_close_without_measurements_writes_no_file(
     )).json()
     assert closed["statistics_path"] is None
     assert not (tmp_path / "statistics").exists()
+
+
+async def test_statistics_csv_writes_nan_value_and_deviation(
+    client: AsyncClient, measurement_tec_user, admin_user, db_session,
+):
+    """#124: una quota NaN (value NULL) esce NaN sia nel valore sia nella deviazione."""
+    from src.backend.services import measurement_service, production_export_service
+
+    station = await _station(db_session, admin_user.id, code="ST-NAN")
+    recipe = await _recipe_with_interval(db_session, admin_user.id, 10, code="REC-NAN")
+    opened = (await _open(client, measurement_tec_user, station, recipe)).json()
+    subtask = await _first_subtask(db_session, recipe.id)
+    await measurement_service.save_measurement(
+        db_session, subtask_id=subtask.id, version_id=opened["version_id"],
+        measured_by=measurement_tec_user.id, value=None, input_method="camera",
+        production_run_id=opened["id"], enforce_tolerance_gate=False,
+    )
+    await db_session.commit()
+    run = (await db_session.execute(
+        select(ProductionRun).where(ProductionRun.id == opened["id"])
+    )).scalar_one()
+
+    text = await production_export_service.build_statistics_csv(db_session, run)
+    lines = [line for line in text.lstrip("").splitlines() if line.strip()]
+    header = lines[0].split(",")
+    row = lines[1].split(",")
+    assert row[header.index("value")] == "NaN"
+    assert row[header.index("deviation")] == "NaN"