diff --git a/freqtrade/data/btanalysis.py b/freqtrade/data/btanalysis.py
index d1884d00c..fe85b08ea 100644
--- a/freqtrade/data/btanalysis.py
+++ b/freqtrade/data/btanalysis.py
@@ -404,12 +404,13 @@ def load_backtest_data(filename: Path | str, strategy: str | None = None) -> pd.
     return df
 
 
-def load_file_from_zip(zip_path: Path, filename: str) -> bytes | None:
+def load_file_from_zip(zip_path: Path, filename: str) -> bytes:
     """
     Load a file from a zip file
     :param zip_path: Path to the zip file
     :param filename: Name of the file to load
     :return: Bytes of the file
+    :raises: ValueError if loading goes wrong.
     """
     try:
         with zipfile.ZipFile(zip_path) as zipf:
@@ -417,7 +418,7 @@ def load_file_from_zip(zip_path: Path, filename: str) -> bytes | None:
                 return file.read()
     except zipfile.BadZipFile:
         logger.exception(f"Bad zip file: {zip_path}")
-        return None
+        raise ValueError(f"Bad zip file: {zip_path}") from None
 
 
 def load_backtest_analysis_data(backtest_dir: Path, name: str):
diff --git a/freqtrade/optimize/optimize_reports/bt_storage.py b/freqtrade/optimize/optimize_reports/bt_storage.py
index b6b110638..d0c5d7fb7 100644
--- a/freqtrade/optimize/optimize_reports/bt_storage.py
+++ b/freqtrade/optimize/optimize_reports/bt_storage.py
@@ -1,7 +1,7 @@
 import logging
 from io import BytesIO, StringIO
 from pathlib import Path
-from typing import Any, TextIO
+from typing import Any
 from zipfile import ZIP_DEFLATED, ZipFile
 
 from pandas import DataFrame
@@ -16,7 +16,7 @@ from freqtrade.optimize.backtest_caching import get_backtest_metadata_filename
 logger = logging.getLogger(__name__)
 
 
-def file_dump_joblib(file_obj: TextIO, data: Any, log: bool = True) -> None:
+def file_dump_joblib(file_obj: BytesIO, data: Any, log: bool = True) -> None:
     """
     Dump object data into a file
     :param filename: file to create