diff --git a/axes/attempts.py b/axes/attempts.py
index a47eb60..9ab40be 100644
--- a/axes/attempts.py
+++ b/axes/attempts.py
@@ -1,5 +1,5 @@
 from logging import getLogger
-from typing import List
+from typing import List, Optional
 
 from django.db.models import QuerySet
 from django.utils.timezone import datetime, now
@@ -11,7 +11,7 @@ from axes.models import AccessAttempt
 log = getLogger(__name__)
 
 
-def get_cool_off_threshold(attempt_time: datetime = None) -> datetime:
+def get_cool_off_threshold(attempt_time: Optional[datetime] = None) -> datetime:
     """
     Get threshold for fetching access attempts from the database.
     """
@@ -27,7 +27,7 @@ def get_cool_off_threshold(attempt_time: datetime = None) -> datetime:
     return attempt_time - cool_off
 
 
-def filter_user_attempts(request, credentials: dict = None) -> List[QuerySet]:
+def filter_user_attempts(request, credentials: Optional[dict] = None) -> List[QuerySet]:
     """
     Return a list querysets of AccessAttempts that match the given request and credentials.
     """
@@ -44,7 +44,7 @@ def filter_user_attempts(request, credentials: dict = None) -> List[QuerySet]:
     return attempts_list
 
 
-def get_user_attempts(request, credentials: dict = None) -> List[QuerySet]:
+def get_user_attempts(request, credentials: Optional[dict] = None) -> List[QuerySet]:
     """
     Get list of querysets with valid user attempts that match the given request and credentials.
     """
@@ -62,7 +62,7 @@ def get_user_attempts(request, credentials: dict = None) -> List[QuerySet]:
     return [attempts.filter(attempt_time__gte=threshold) for attempts in attempts_list]
 
 
-def clean_expired_user_attempts(attempt_time: datetime = None) -> int:
+def clean_expired_user_attempts(attempt_time: Optional[datetime] = None) -> int:
     """
     Clean expired user attempts from the database.
     """
@@ -83,7 +83,7 @@ def clean_expired_user_attempts(attempt_time: datetime = None) -> int:
     return count
 
 
-def reset_user_attempts(request, credentials: dict = None) -> int:
+def reset_user_attempts(request, credentials: Optional[dict] = None) -> int:
     """
     Reset all user attempts that match the given request and credentials.
     """
diff --git a/axes/backends.py b/axes/backends.py
index c337f89..30535f3 100644
--- a/axes/backends.py
+++ b/axes/backends.py
@@ -1,3 +1,4 @@
+from typing import Optional
 from django.conf import settings
 from django.contrib.auth.backends import ModelBackend
 
@@ -22,7 +23,7 @@ class AxesBackend(ModelBackend):
 
     @toggleable
     def authenticate(
-        self, request, username: str = None, password: str = None, **kwargs: dict
+        self, request, username: Optional[str] = None, password: Optional[str] = None, **kwargs: dict
     ):
         """
         Checks user lockout status and raises an exception if user is not allowed to log in.
diff --git a/axes/handlers/base.py b/axes/handlers/base.py
index 59b715d..f2643c4 100644
--- a/axes/handlers/base.py
+++ b/axes/handlers/base.py
@@ -1,5 +1,6 @@
 import re
 from abc import ABC, abstractmethod
+from typing import Optional
 
 from django.urls import reverse
 from django.urls.exceptions import NoReverseMatch
@@ -41,7 +42,7 @@ class AbstractAxesHandler(ABC):
         raise NotImplementedError("user_logged_out should be implemented")
 
     @abstractmethod
-    def get_failures(self, request, credentials: dict = None) -> int:
+    def get_failures(self, request, credentials: Optional[dict] = None) -> int:
         """
         Checks the number of failures associated to the given request and credentials.
 
@@ -65,7 +66,7 @@ class AxesBaseHandler:  # pylint: disable=unused-argument
     .. note:: This is a virtual class and **can not be used without specialization**.
     """
 
-    def is_allowed(self, request, credentials: dict = None) -> bool:
+    def is_allowed(self, request, credentials: Optional[dict] = None) -> bool:
         """
         Checks if the user is allowed to access or use given functionality such as a login view or authentication.
 
@@ -94,7 +95,7 @@ class AxesBaseHandler:  # pylint: disable=unused-argument
 
         return True
 
-    def is_blacklisted(self, request, credentials: dict = None) -> bool:
+    def is_blacklisted(self, request, credentials: Optional[dict] = None) -> bool:
         """
         Checks if the request or given credentials are blacklisted from access.
         """
@@ -104,7 +105,7 @@ class AxesBaseHandler:  # pylint: disable=unused-argument
 
         return False
 
-    def is_whitelisted(self, request, credentials: dict = None) -> bool:
+    def is_whitelisted(self, request, credentials: Optional[dict] = None) -> bool:
         """
         Checks if the request or given credentials are whitelisted for access.
         """
@@ -120,7 +121,7 @@ class AxesBaseHandler:  # pylint: disable=unused-argument
 
         return False
 
-    def is_locked(self, request, credentials: dict = None) -> bool:
+    def is_locked(self, request, credentials: Optional[dict] = None) -> bool:
         """
         Checks if the request or given credentials are locked.
         """
@@ -149,8 +150,8 @@ class AxesBaseHandler:  # pylint: disable=unused-argument
     def reset_attempts(
         self,
         *,
-        ip_address: str = None,
-        username: str = None,
+        ip_address: Optional[str] = None,
+        username: Optional[str] = None,
         ip_or_username: bool = False,
     ) -> int:
         """
@@ -163,7 +164,7 @@ class AxesBaseHandler:  # pylint: disable=unused-argument
         """
         return 0
 
-    def reset_logs(self, *, age_days: int = None) -> int:
+    def reset_logs(self, *, age_days: Optional[int] = None) -> int:
         """
         Resets access logs that are older than given number of days.
 
@@ -174,7 +175,7 @@ class AxesBaseHandler:  # pylint: disable=unused-argument
         """
         return 0
 
-    def reset_failure_logs(self, *, age_days: int = None) -> int:
+    def reset_failure_logs(self, *, age_days: Optional[int] = None) -> int:
         """
         Resets access failure logs that are older than given number of days.
 
@@ -186,7 +187,7 @@ class AxesBaseHandler:  # pylint: disable=unused-argument
         return 0
 
 
-    def remove_out_of_limit_failure_logs(self, *, username: str, limit: int = None) -> int:
+    def remove_out_of_limit_failure_logs(self, *, username: str, limit: Optional[int] = None) -> int:
         """Remove access failure logs that are over
         AXES_ACCESS_FAILURE_LOG_PER_USER_LIMIT for user username.
 
@@ -212,5 +213,5 @@ class AxesHandler(AbstractAxesHandler, AxesBaseHandler):
     def user_logged_out(self, sender, request, user, **kwargs):
         pass
 
-    def get_failures(self, request, credentials: dict = None) -> int:
+    def get_failures(self, request, credentials: Optional[dict] = None) -> int:
         return 0
diff --git a/axes/handlers/cache.py b/axes/handlers/cache.py
index 8bddae1..423c592 100644
--- a/axes/handlers/cache.py
+++ b/axes/handlers/cache.py
@@ -1,4 +1,5 @@
 from logging import getLogger
+from typing import Optional
 
 from axes.conf import settings
 from axes.handlers.base import AxesBaseHandler, AbstractAxesHandler
@@ -56,7 +57,7 @@ class AxesCacheHandler(AbstractAxesHandler, AxesBaseHandler):
 
         return count
 
-    def get_failures(self, request, credentials: dict = None) -> int:
+    def get_failures(self, request, credentials: Optional[dict] = None) -> int:
         cache_keys = get_client_cache_key(request, credentials)
         failure_count = max(
             self.cache.get(cache_key, default=0) for cache_key in cache_keys
diff --git a/axes/handlers/database.py b/axes/handlers/database.py
index 176c898..5ac0843 100644
--- a/axes/handlers/database.py
+++ b/axes/handlers/database.py
@@ -1,4 +1,5 @@
 from logging import getLogger
+from typing import Optional
 
 from django.db import transaction
 from django.db.models import F, Sum, Value, Q
@@ -36,8 +37,8 @@ class AxesDatabaseHandler(AbstractAxesHandler, AxesBaseHandler):
     def reset_attempts(
         self,
         *,
-        ip_address: str = None,
-        username: str = None,
+        ip_address: Optional[str] = None,
+        username: Optional[str] = None,
         ip_or_username: bool = False,
     ) -> int:
         attempts = AccessAttempt.objects.all()
@@ -55,7 +56,7 @@ class AxesDatabaseHandler(AbstractAxesHandler, AxesBaseHandler):
 
         return count
 
-    def reset_logs(self, *, age_days: int = None) -> int:
+    def reset_logs(self, *, age_days: Optional[int] = None) -> int:
         if age_days is None:
             count, _ = AccessLog.objects.all().delete()
             log.info("AXES: Reset all %d access logs from database.", count)
@@ -70,7 +71,7 @@ class AxesDatabaseHandler(AbstractAxesHandler, AxesBaseHandler):
 
         return count
 
-    def reset_failure_logs(self, *, age_days: int = None) -> int:
+    def reset_failure_logs(self, *, age_days: Optional[int] = None) -> int:
         if age_days is None:
             count, _ = AccessFailureLog.objects.all().delete()
             log.info("AXES: Reset all %d access failure logs from database.", count)
@@ -89,7 +90,7 @@ class AxesDatabaseHandler(AbstractAxesHandler, AxesBaseHandler):
             self,
             *,
             username: str,
-            limit: int = settings.AXES_ACCESS_FAILURE_LOG_PER_USER_LIMIT) -> int:
+            limit: Optional[int] = settings.AXES_ACCESS_FAILURE_LOG_PER_USER_LIMIT) -> int:
         count = 0
         failures = AccessFailureLog.objects.filter(username=username)
         out_of_limit_failures_logs = failures.count() - limit
@@ -99,7 +100,7 @@ class AxesDatabaseHandler(AbstractAxesHandler, AxesBaseHandler):
                 count += 1
         return count
 
-    def get_failures(self, request, credentials: dict = None) -> int:
+    def get_failures(self, request, credentials: Optional[dict] = None) -> int:
         attempts_list = get_user_attempts(request, credentials)
         attempt_count = max(
             (
diff --git a/axes/handlers/dummy.py b/axes/handlers/dummy.py
index 0e40ace..b8c3bbb 100644
--- a/axes/handlers/dummy.py
+++ b/axes/handlers/dummy.py
@@ -1,4 +1,5 @@
 from axes.handlers.base import AxesBaseHandler, AbstractAxesHandler
+from typing import Optional
 
 
 class AxesDummyHandler(AbstractAxesHandler, AxesBaseHandler):
@@ -6,7 +7,7 @@ class AxesDummyHandler(AbstractAxesHandler, AxesBaseHandler):
     Signal handler implementation that does nothing and can be used to disable signal processing.
     """
 
-    def is_allowed(self, request, credentials: dict = None) -> bool:
+    def is_allowed(self, request, credentials: Optional[dict] = None) -> bool:
         return True
 
     def user_login_failed(self, sender, credentials: dict, request=None, **kwargs):
@@ -18,5 +19,5 @@ class AxesDummyHandler(AbstractAxesHandler, AxesBaseHandler):
     def user_logged_out(self, sender, request, user, **kwargs):
         pass
 
-    def get_failures(self, request, credentials: dict = None) -> int:
+    def get_failures(self, request, credentials: Optional[dict] = None) -> int:
         return 0
diff --git a/axes/handlers/proxy.py b/axes/handlers/proxy.py
index 8c0a3f3..1adebe1 100644
--- a/axes/handlers/proxy.py
+++ b/axes/handlers/proxy.py
@@ -1,4 +1,5 @@
 from logging import getLogger
+from typing import Optional
 
 from django.utils.module_loading import import_string
 from django.utils.timezone import now
@@ -46,8 +47,8 @@ class AxesProxyHandler(AbstractAxesHandler, AxesBaseHandler):
     def reset_attempts(
         cls,
         *,
-        ip_address: str = None,
-        username: str = None,
+        ip_address: Optional[str] = None,
+        username: Optional[str] = None,
         ip_or_username: bool = False,
     ) -> int:
         return cls.get_implementation().reset_attempts(
@@ -55,15 +56,15 @@ class AxesProxyHandler(AbstractAxesHandler, AxesBaseHandler):
         )
 
     @classmethod
-    def reset_logs(cls, *, age_days: int = None) -> int:
+    def reset_logs(cls, *, age_days: Optional[int] = None) -> int:
         return cls.get_implementation().reset_logs(age_days=age_days)
 
     @classmethod
-    def reset_failure_logs(cls, *, age_days: int = None) -> int:
+    def reset_failure_logs(cls, *, age_days: Optional[int] = None) -> int:
         return cls.get_implementation().reset_failure_logs(age_days=age_days)
 
     @classmethod
-    def remove_out_of_limit_failure_logs(cls, *, username: str, limit: int = None) -> int:
+    def remove_out_of_limit_failure_logs(cls, *, username: str, limit: Optional[int] = None) -> int:
         return cls.get_implementation().remove_out_of_limit_failure_logs(username=username)
 
     @staticmethod
@@ -90,17 +91,17 @@ class AxesProxyHandler(AbstractAxesHandler, AxesBaseHandler):
             request.axes_credentials = None
 
     @classmethod
-    def is_locked(cls, request, credentials: dict = None) -> bool:
+    def is_locked(cls, request, credentials: Optional[dict] = None) -> bool:
         cls.update_request(request)
         return cls.get_implementation().is_locked(request, credentials)
 
     @classmethod
-    def is_allowed(cls, request, credentials: dict = None) -> bool:
+    def is_allowed(cls, request, credentials: Optional[dict] = None) -> bool:
         cls.update_request(request)
         return cls.get_implementation().is_allowed(request, credentials)
 
     @classmethod
-    def get_failures(cls, request, credentials: dict = None) -> int:
+    def get_failures(cls, request, credentials: Optional[dict] = None) -> int:
         cls.update_request(request)
         return cls.get_implementation().get_failures(request, credentials)
 
diff --git a/axes/handlers/test.py b/axes/handlers/test.py
index c345104..bea66b3 100644
--- a/axes/handlers/test.py
+++ b/axes/handlers/test.py
@@ -1,4 +1,5 @@
 from axes.handlers.base import AxesHandler
+from typing import Optional
 
 
 class AxesTestHandler(AxesHandler):  # pylint: disable=unused-argument
@@ -9,17 +10,17 @@ class AxesTestHandler(AxesHandler):  # pylint: disable=unused-argument
     def reset_attempts(
         self,
         *,
-        ip_address: str = None,
-        username: str = None,
+        ip_address: Optional[str] = None,
+        username: Optional[str] = None,
         ip_or_username: bool = False,
     ) -> int:
         return 0
 
-    def reset_logs(self, *, age_days: int = None) -> int:
+    def reset_logs(self, *, age_days: Optional[int] = None) -> int:
         return 0
 
-    def is_allowed(self, request, credentials: dict = None) -> bool:
+    def is_allowed(self, request, credentials: Optional[dict] = None) -> bool:
         return True
 
-    def get_failures(self, request, credentials: dict = None) -> int:
+    def get_failures(self, request, credentials: Optional[dict] = None) -> int:
         return 0
diff --git a/axes/helpers.py b/axes/helpers.py
index 3061614..18a3aa8 100644
--- a/axes/helpers.py
+++ b/axes/helpers.py
@@ -90,7 +90,7 @@ def get_cool_off_iso8601(delta: timedelta) -> str:
     return f"P{days_str}"
 
 
-def get_credentials(username: str = None, **kwargs) -> dict:
+def get_credentials(username: Optional[str] = None, **kwargs) -> dict:
     """
     Calculate credentials for Axes to use internally from given username and kwargs.
 
@@ -103,7 +103,7 @@ def get_credentials(username: str = None, **kwargs) -> dict:
     return credentials
 
 
-def get_client_username(request, credentials: dict = None) -> str:
+def get_client_username(request, credentials: Optional[dict] = None) -> str:
     """
     Resolve client username from the given request or credentials if supplied.
 
@@ -218,7 +218,7 @@ def make_cache_key_list(filter_kwargs_list):
 
 
 def get_client_cache_key(
-    request_or_attempt: Union[HttpRequest, AccessBase], credentials: dict = None
+    request_or_attempt: Union[HttpRequest, AccessBase], credentials: Optional[dict] = None
 ) -> str:
     """
     Build cache key name from request or AccessAttempt object.
@@ -360,7 +360,7 @@ def get_lockout_message() -> str:
     return settings.AXES_PERMALOCK_MESSAGE
 
 
-def get_lockout_response(request, credentials: dict = None) -> HttpResponse:
+def get_lockout_response(request, credentials: Optional[dict] = None) -> HttpResponse:
     if settings.AXES_LOCKOUT_CALLABLE:
         if callable(settings.AXES_LOCKOUT_CALLABLE):
             return settings.AXES_LOCKOUT_CALLABLE(  # pylint: disable=not-callable
@@ -475,7 +475,7 @@ def is_client_method_whitelisted(request) -> bool:
     return False
 
 
-def is_user_attempt_whitelisted(request, credentials: dict = None) -> bool:
+def is_user_attempt_whitelisted(request, credentials: Optional[dict] = None) -> bool:
     """
     Check if the given request or credentials refer to a whitelisted username.
 
diff --git a/axes/utils.py b/axes/utils.py
index 2cdd9d7..824fc9c 100644
--- a/axes/utils.py
+++ b/axes/utils.py
@@ -17,7 +17,7 @@ from axes.helpers import get_client_ip_address
 log = getLogger(__name__)
 
 
-def reset(ip: str = None, username: str = None, ip_or_username=False) -> int:
+def reset(ip: Optional[str] = None, username: Optional[str] = None, ip_or_username=False) -> int:
     """
     Reset records that match IP or username, and return the count of removed attempts.