diff --git a/src/frontend/flask_app/templates/measure/task_execute.html b/src/frontend/flask_app/templates/measure/task_execute.html
index 15995e4..4ecbb1a 100644
--- a/src/frontend/flask_app/templates/measure/task_execute.html
+++ b/src/frontend/flask_app/templates/measure/task_execute.html
@@ -926,8 +926,8 @@ function taskExecute() {
     // ---- Data from server ----
     task: window.__taskData,
     subtasks: window.__taskSubtasks,
-    lotNumber: '{{ lot_number or '' }}',
-    serialNumber: '{{ serial_number or '' }}',
+    lotNumber: {{ (lot_number or '')|tojson }},
+    serialNumber: {{ (serial_number or '')|tojson }},
     // ---- Measurement state ----
     currentIndex: 0,
     measurements: [],   // [{subtask_id, value, pass_fail, deviation}, ...]
diff --git a/src/frontend/flask_app/tests/test_task_execute_lot_tojson.py b/src/frontend/flask_app/tests/test_task_execute_lot_tojson.py
new file mode 100644
index 0000000..4b03825
--- /dev/null
+++ b/src/frontend/flask_app/tests/test_task_execute_lot_tojson.py
@@ -0,0 +1,89 @@
+"""gitea:Adriano/TieMeasureFlow#32.
+
+lotNumber/serialNumber used to be interpolated into task_execute.html's
+<script> block as a quoted JS string literal (``'{{ lot_number or '' }}'``),
+which relies on Jinja's *HTML* autoescaping - the wrong escaping for a value
+that has to be valid *inside a <script> block*. A lot number containing ``&``
+came back HTML-entity-escaped (``A&amp;B-12``) instead of the literal
+character, silently corrupting the value sent to the server on every
+measurement and on production/start. A lot ending in a backslash produced
+invalid JavaScript outright.
+
+``|tojson`` is the fix: it produces a JSON literal, safe both as JS source
+and as HTML, matching how every other user-supplied value on this page is
+already embedded (see ``refuseWhileBlocked()``'s comment on the same file).
+"""
+from tests.conftest import api_get_router
+
+TASK = {
+    "id": 11,
+    "recipe_id": 3,
+    "version_id": 5,
+    "task_type": "measure",
+    "title": "Quota",
+    "directive": None,
+    "description": None,
+    "file_path": None,
+    "file_type": None,
+    "annotations_json": None,
+    "subtasks": [{
+        "id": 21, "marker_number": 1, "description": "Altezza", "order_index": 0,
+        "nominal": 10.0, "utl": 10.5, "uwl": 10.2, "lwl": 9.8, "ltl": 9.5,
+        "unit": "mm",
+    }],
+}
+
+RECIPE = {
+    "id": 3, "code": "REC-1", "name": "Ricetta",
+    "measurement_interval_minutes": 30, "allow_manual_input": True,
+    "current_version": {"id": 5, "version_number": 1},
+}
+
+
+def _execute_page(client, mock_api_client, monkeypatch, lot_number, serial_number):
+    with client.session_transaction() as sess:
+        sess["language"] = "it"
+        sess["lot_number"] = lot_number
+        sess["serial_number"] = serial_number
+    # task_execute() only renders a recipe assigned to this station (#24);
+    # not what #32 is about, but the route 403s without it.
+    monkeypatch.setattr("blueprints.measure.Config.STATION_CODE", "ST-TEST")
+    mock_api_client.get_station_recipes.return_value = {"items": [{"id": 3}]}
+    mock_api_client.get.side_effect = api_get_router({
+        "/api/tasks/11": TASK,
+        "/api/recipes/3/tasks": [{"id": 11, "order_index": 0}],
+        "/api/recipes/3": RECIPE,
+    })
+    resp = client.get("/measure/execute/11")
+    assert resp.status_code == 200
+    return resp.get_data(as_text=True)
+
+
+def test_ampersand_in_lot_number_is_not_html_escaped(logged_in_client, mock_api_client, monkeypatch):
+    html = _execute_page(logged_in_client, mock_api_client, monkeypatch, "A&B-12", "S1")
+
+    # The old bug, scoped to the <script> data block: the JS literal for
+    # lotNumber must not carry HTML-entity escaping (that is correct for the
+    # plain-text display of the same value elsewhere on the page, but breaks
+    # the value actually sent to the server on every measurement).
+    assert 'lotNumber: "A&amp;B-12"' not in html
+    # tojson's escaping for "&" is the \uXXXX form.
+    assert 'lotNumber: "A\\u0026B-12"' in html
+
+
+def test_backslash_in_serial_number_stays_valid_json(logged_in_client, mock_api_client, monkeypatch):
+    # The old literal '{{ serial_number or '' }}' would end with a bare
+    # backslash escaping the closing quote - a SyntaxError, not merely a
+    # wrong value. tojson escapes it instead.
+    html = _execute_page(logged_in_client, mock_api_client, monkeypatch, "L1", "LOT\\")
+
+    assert 'serialNumber: "LOT\\\\"' in html
+
+
+def test_apostrophe_in_lot_number_stays_a_single_json_string(logged_in_client, mock_api_client, monkeypatch):
+    # The old literal '{{ lot_number or '' }}' would have closed its own
+    # quoted string early on the apostrophe. tojson escapes it to ',
+    # which the JS engine reads back as the same original character.
+    html = _execute_page(logged_in_client, mock_api_client, monkeypatch, "O'Brien-7", "S2")
+
+    assert 'lotNumber: "O\\u0027Brien-7"' in html