diff --git a/libmat2/abstract.py b/libmat2/abstract.py
index e4838a9f943c5ebd4f5339aafa0fd5f0f0705069..9cb93206e814c37870a175c8589079fb5f004f04 100644
--- a/libmat2/abstract.py
+++ b/libmat2/abstract.py
@@ -1,12 +1,13 @@
 import abc
 import os
+from typing import Set
 
 
 class AbstractParser(abc.ABC):
-    meta_list = set()
-    mimetypes = set()
+    meta_list = set()  # type: Set[str]
+    mimetypes = set()  # type: Set[str]
 
-    def __init__(self, filename: str):
+    def __init__(self, filename: str) -> None:
         self.filename = filename
         fname, extension = os.path.splitext(filename)
         self.output_filename = fname + '.cleaned' + extension
diff --git a/libmat2/harmless.py b/libmat2/harmless.py
index aa00582ccbd38874361395244188375a52200309..a63407f78513d198427d025738caae082343bd4a 100644
--- a/libmat2/harmless.py
+++ b/libmat2/harmless.py
@@ -5,7 +5,7 @@ class HarmlessParser(abstract.AbstractParser):
     """ This is the parser for filetypes that do not contain metadata. """
     mimetypes = {'application/xml', 'text/plain'}
 
-    def __init__(self, filename: str):
+    def __init__(self, filename: str) -> None:
         super().__init__(filename)
         self.filename = filename
         self.output_filename = filename
diff --git a/libmat2/torrent.py b/libmat2/torrent.py
index cb4b5e3fa0ae581cd76df32502636fea9f17a95a..3a819fb1890d55c5cb8ed1aaffa1a459e7e9ef53 100644
--- a/libmat2/torrent.py
+++ b/libmat2/torrent.py
@@ -2,7 +2,7 @@ from . import abstract
 
 
 class TorrentParser(abstract.AbstractParser):
-    mimetypes = {'application/x-bittorrent', }
+    mimetypes = {b'application/x-bittorrent', }
     whitelist = {b'announce', b'announce-list', b'info'}
 
     def get_meta(self) -> dict: