diff --git a/fastf1/_api.py b/fastf1/_api.py
index 535003a37..7676c53cc 100644
--- a/fastf1/_api.py
+++ b/fastf1/_api.py
@@ -892,10 +892,10 @@ def timing_app_data(path, response=None, livedata=None):
         row = entry[1]
         for driver_number in row['Lines']:
             if update := recursive_dict_get(row, 'Lines', driver_number, 'Stints'):
-                for stint_number, stint in enumerate(update):
-                    if isinstance(update, dict):
-                        stint_number = int(stint)
-                        stint = update[stint]
+                if isinstance(update, list):
+                    update = {str(i): s for i, s in enumerate(update)}
+                for stint_number, stint in update.items():
+                    stint_number = int(stint_number)
                     for key in data:
                         if key in stint:
                             val = stint[key]
diff --git a/fastf1/tests/test_api.py b/fastf1/tests/test_api.py
index 8c3c78728..ee170db11 100644
--- a/fastf1/tests/test_api.py
+++ b/fastf1/tests/test_api.py
@@ -266,6 +266,68 @@ def test_driver_list_contains_support_race(caplog):
     _, _, warn_message = caplog.record_tuples[0]
     assert warn_message.startswith("Skipping delayed declaration of driver")
 
+def test_timing_app_data_legacy_list_format():
+    """Stints in list format (legacy API, ~2018-2019) must be parsed correctly.
+    
+    Historic races return stints as a plain list instead of a dict with
+    string indices. Previously, this caused stints to be silently dropped.
+    See issue #863.
+    """
+    response = [
+        [
+            "00:05:00:000",
+            {
+                "Lines": {
+                    "1": {
+                        "Stints": [
+                            {"Compound": "SOFT", "New": "true",
+                             "TotalLaps": 0, "StartLaps": 0},
+                            {"Compound": "HARD", "New": "false",
+                             "TotalLaps": 10, "StartLaps": 10},
+                        ]
+                    }
+                }
+            }
+        ]
+    ]
+
+    data = fastf1._api.timing_app_data('api/path', response=response)
+
+    assert isinstance(data, pd.DataFrame)
+    assert len(data) == 2  # both stints must be present
+    assert list(data['Stint']) == [0, 1]
+    assert list(data['Compound']) == ['SOFT', 'HARD']
+    assert list(data['Driver']) == ['1', '1']
+
+
+def test_timing_app_data_modern_dict_format():
+    """Stints in dict format (modern API) must continue to work correctly."""
+    response = [
+        [
+            "00:05:00:000",
+            {
+                "Lines": {
+                    "1": {
+                        "Stints": {
+                            "0": {"Compound": "MEDIUM", "New": "true",
+                                  "TotalLaps": 0, "StartLaps": 0},
+                            "1": {"Compound": "HARD", "New": "false",
+                                  "TotalLaps": 20, "StartLaps": 20},
+                        }
+                    }
+                }
+            }
+        ]
+    ]
+
+    data = fastf1._api.timing_app_data('api/path', response=response)
+
+    assert isinstance(data, pd.DataFrame)
+    assert len(data) == 2  # both stints must be present
+    assert list(data['Stint']) == [0, 1]
+    assert list(data['Compound']) == ['MEDIUM', 'HARD']
+    assert list(data['Driver']) == ['1', '1']
+
 @pytest.mark.f1telapi
 def test_deleted_laps_not_marked_personal_best():
     # see issue #165