diff --git a/knox/auth.py b/knox/auth.py
index bf3749e2..ffb0880b 100644
--- a/knox/auth.py
+++ b/knox/auth.py
@@ -71,7 +71,7 @@ def authenticate_credentials(self, token):
                 return self.validate_user(auth_token)
         raise exceptions.AuthenticationFailed(msg)
 
-    def renew_token(self, auth_token):
+    def renew_token(self, auth_token) -> None:
         current_expiry = auth_token.expiry
         new_expiry = timezone.now() + knox_settings.TOKEN_TTL
         auth_token.expiry = new_expiry
@@ -89,7 +89,7 @@ def validate_user(self, auth_token):
     def authenticate_header(self, request):
         return knox_settings.AUTH_HEADER_PREFIX
 
-    def _cleanup_token(self, auth_token):
+    def _cleanup_token(self, auth_token) -> bool:
         for other_token in auth_token.user.auth_token_set.all():
             if other_token.digest != auth_token.digest and other_token.expiry:
                 if other_token.expiry < timezone.now():
diff --git a/knox/crypto.py b/knox/crypto.py
index 1ee36146..02e70ffe 100644
--- a/knox/crypto.py
+++ b/knox/crypto.py
@@ -6,13 +6,13 @@
 hash_func = knox_settings.SECURE_HASH_ALGORITHM
 
 
-def create_token_string():
+def create_token_string() -> str:
     return binascii.hexlify(
         generate_bytes(int(knox_settings.AUTH_TOKEN_CHARACTER_LENGTH / 2))
     ).decode()
 
 
-def make_hex_compatible(token: str) -> str:
+def make_hex_compatible(token: str) -> bytes:
     """
     We need to make sure that the token, that is send is hex-compatible.
     When a token prefix is used, we cannot guarantee that.
diff --git a/knox/models.py b/knox/models.py
index b054f289..80929bcf 100644
--- a/knox/models.py
+++ b/knox/models.py
@@ -48,7 +48,7 @@ class AbstractAuthToken(models.Model):
     class Meta:
         abstract = True
 
-    def __str__(self):
+    def __str__(self) -> str:
         return '%s : %s' % (self.digest, self.user)
 
 
diff --git a/knox/settings.py b/knox/settings.py
index a5def499..d1b09347 100644
--- a/knox/settings.py
+++ b/knox/settings.py
@@ -55,4 +55,4 @@ def __setattr__(self, *args, **kwargs):
             ''')
 
 
-CONSTANTS = CONSTANTS()
+CONSTANTS = CONSTANTS()  # type: ignore