diff --git a/python/src/functions/generate_treasury_report.py b/python/src/functions/generate_treasury_report.py
index ab7c7604..2f01f92d 100644
--- a/python/src/functions/generate_treasury_report.py
+++ b/python/src/functions/generate_treasury_report.py
@@ -229,7 +229,7 @@ def process_event(payload: ProjectLambdaPayload, logger: structlog.stdlib.BoundL
                 file=new_output_file,
             )
         # Output CSV file for treasury
-        with tempfile.NamedTemporaryFile("rb+") as csv_file:
+        with tempfile.NamedTemporaryFile("r+") as csv_file:
             convert_xlsx_to_csv(csv_file, output_workbook, highest_row_num)
             upload_generated_file_to_s3(
                 client=s3_client,
diff --git a/python/src/lib/workbook_utils.py b/python/src/lib/workbook_utils.py
index 6aa87ab9..77143c8f 100644
--- a/python/src/lib/workbook_utils.py
+++ b/python/src/lib/workbook_utils.py
@@ -1,6 +1,6 @@
 import csv
 from tempfile import _TemporaryFileWrapper
-from typing import IO, Optional, Union
+from typing import Optional
 
 from openpyxl import Workbook
 from openpyxl.worksheet.worksheet import Worksheet
@@ -19,8 +19,8 @@ def escape_for_csv(text: Optional[str]):
 
 
 def convert_xlsx_to_csv(
-    csv_file: Union[IO[bytes], _TemporaryFileWrapper],
-    file: Union[IO[bytes], Workbook],
+    csv_file: "_TemporaryFileWrapper[str]",
+    file: Workbook,
     num_rows: int,
 ):
     """