diff --git a/library/jpeg_xl_util.py b/library/jpeg_xl_util.py
index d127d44d..3f5e7f72 100644
--- a/library/jpeg_xl_util.py
+++ b/library/jpeg_xl_util.py
@@ -1,15 +1,17 @@
 # Modified from https://github.com/Fraetor/jxl_decode
 # Added partial read support for up to 200x speedup
+
 import os
+from typing import List, Tuple
 
 class JXLBitstream:
     """
     A stream of bits with methods for easy handling.
     """
 
-    def __init__(self, file, offset=0, offsets=[]) -> None:
+    def __init__(self, file, offset: int = 0, offsets: List[List[int]] = None):
         self.shift = 0
-        self.bitstream = []
+        self.bitstream = bytearray()
         self.file = file
         self.offset = offset
         self.offsets = offsets
@@ -32,7 +34,7 @@ class JXLBitstream:
         self.shift += length
         return bits
 
-    def partial_read(self, current_length, length):
+    def partial_read(self, current_length: int, length: int) -> None:
         self.previous_data_len += self.offsets[self.index][2]
         to_read_length = self.previous_data_len - (self.shift + current_length)
         self.bitstream += self.file.read(to_read_length)
@@ -44,7 +46,7 @@ class JXLBitstream:
             self.partial_read(current_length, length)
 
 
-def decode_codestream(file, offset=0, offsets=[]):
+def decode_codestream(file, offset: int = 0, offsets: List[List[int]] = None) -> Tuple[int,int]:
     """
     Decodes the actual codestream.
     JXL codestream specification: http://www-internal/2022/18181-1
@@ -104,13 +106,13 @@ def decode_codestream(file, offset=0, offsets=[]):
     return width, height
 
 
-def decode_container(file):
+def decode_container(file) -> Tuple[int,int]:
     """
     Parses the ISOBMFF container, extracts the codestream, and decodes it.
     JXL container specification: http://www-internal/2022/18181-2
     """
 
-    def parse_box(file, file_start) -> dict:
+    def parse_box(file, file_start: int) -> dict:
         file.seek(file_start)
         LBox = int.from_bytes(file.read(4), "big")
         XLBox = None
@@ -177,7 +179,7 @@ def decode_container(file):
     return decode_codestream(file, offset=offset, offsets=offsets)
 
 
-def get_jxl_size(path):
+def get_jxl_size(path: str) -> Tuple[int,int]:
     with open(path, "rb") as file:
         if file.read(2) == bytes.fromhex("FF0A"):
             return decode_codestream(file)