diff --git a/posthog/temporal/batch_exports/s3_batch_export.py b/posthog/temporal/batch_exports/s3_batch_export.py
index 55dacb59e60e4..8246db39eb6ad 100644
--- a/posthog/temporal/batch_exports/s3_batch_export.py
+++ b/posthog/temporal/batch_exports/s3_batch_export.py
@@ -49,6 +49,7 @@
 )
 from posthog.temporal.batch_exports.temporary_file import (
     BatchExportTemporaryFile,
+    UnsupportedFileFormatError,
     WriterFormat,
 )
 from posthog.temporal.batch_exports.utils import set_status_to_running_task
@@ -71,6 +72,8 @@
     "RecordBatchConsumerNonRetryableExceptionGroup",
     # Invalid S3 endpoint URL
     "InvalidS3EndpointError",
+    # Invalid file_format input
+    "UnsupportedFileFormatError",
 ]
 
 FILE_FORMAT_EXTENSIONS = {
@@ -107,7 +110,11 @@ def get_s3_key(inputs) -> str:
     """Return an S3 key given S3InsertInputs."""
     template_variables = get_allowed_template_variables(inputs)
     key_prefix = inputs.prefix.format(**template_variables)
-    file_extension = FILE_FORMAT_EXTENSIONS[inputs.file_format]
+
+    try:
+        file_extension = FILE_FORMAT_EXTENSIONS[inputs.file_format]
+    except KeyError:
+        raise UnsupportedFileFormatError(inputs.file_format, "S3")
 
     base_file_name = f"{inputs.data_interval_start}-{inputs.data_interval_end}"
     if inputs.compression is not None:
diff --git a/posthog/temporal/tests/batch_exports/test_s3_batch_export_workflow.py b/posthog/temporal/tests/batch_exports/test_s3_batch_export_workflow.py
index 3dab18c67b283..85594e7ad4fa0 100644
--- a/posthog/temporal/tests/batch_exports/test_s3_batch_export_workflow.py
+++ b/posthog/temporal/tests/batch_exports/test_s3_batch_export_workflow.py
@@ -39,6 +39,7 @@
     insert_into_s3_activity,
     s3_default_fields,
 )
+from posthog.temporal.batch_exports.temporary_file import UnsupportedFileFormatError
 from posthog.temporal.common.clickhouse import ClickHouseClient
 from posthog.temporal.tests.batch_exports.utils import mocked_start_batch_export_run
 from posthog.temporal.tests.utils.events import generate_test_events_in_clickhouse
@@ -561,6 +562,51 @@ async def test_insert_into_s3_activity_puts_data_into_s3_using_async(
     )
 
 
+@pytest.mark.parametrize("model", [BatchExportModel(name="events", schema=None)])
+@pytest.mark.parametrize("file_format", ["invalid"])
+async def test_insert_into_s3_activity_fails_on_invalid_file_format(
+    clickhouse_client,
+    bucket_name,
+    minio_client,
+    activity_environment,
+    compression,
+    exclude_events,
+    file_format,
+    data_interval_start,
+    data_interval_end,
+    model: BatchExportModel | BatchExportSchema | None,
+    ateam,
+):
+    """Test the insert_into_s3_activity function fails with an invalid file format."""
+    batch_export_schema: BatchExportSchema | None = None
+    batch_export_model: BatchExportModel | None = None
+    if isinstance(model, BatchExportModel):
+        batch_export_model = model
+    elif model is not None:
+        batch_export_schema = model
+
+    insert_inputs = S3InsertInputs(
+        bucket_name=bucket_name,
+        region="us-east-1",
+        prefix="any",
+        team_id=ateam.pk,
+        data_interval_start=data_interval_start.isoformat(),
+        data_interval_end=data_interval_end.isoformat(),
+        aws_access_key_id="object_storage_root_user",
+        aws_secret_access_key="object_storage_root_password",
+        endpoint_url=settings.OBJECT_STORAGE_ENDPOINT,
+        compression=compression,
+        exclude_events=exclude_events,
+        file_format=file_format,
+        batch_export_schema=batch_export_schema,
+        batch_export_model=batch_export_model,
+    )
+
+    with pytest.raises(UnsupportedFileFormatError):
+        with override_settings(BATCH_EXPORT_POSTGRES_UPLOAD_CHUNK_SIZE_BYTES=5 * 1024**2):
+            await activity_environment.run(insert_into_s3_activity, insert_inputs)
+
+
 @pytest_asyncio.fixture
 async def s3_batch_export(
     ateam,