diff --git a/pywidevine/cdm.py b/pywidevine/cdm.py
index db83f45..ce1700f 100644
--- a/pywidevine/cdm.py
+++ b/pywidevine/cdm.py
@@ -638,4 +638,4 @@ def _derive(session_key: bytes, context: bytes, counter: int) -> bytes:
         return enc_key, mac_key_server, mac_key_client
 
 
-__ALL__ = (Cdm,)
+__all__ = ("Cdm",)
diff --git a/pywidevine/device.py b/pywidevine/device.py
index 4625cf5..afa438b 100644
--- a/pywidevine/device.py
+++ b/pywidevine/device.py
@@ -237,4 +237,4 @@ def migrate(cls, data: Union[bytes, str]) -> Device:
             raise ValueError(f"Device Data seems to be corrupt or invalid, or migration failed, {e}")
 
 
-__ALL__ = (Device, DeviceTypes)
+__all__ = ("Device", "DeviceTypes")
diff --git a/pywidevine/key.py b/pywidevine/key.py
index 6b7ff90..c5f8b31 100644
--- a/pywidevine/key.py
+++ b/pywidevine/key.py
@@ -61,3 +61,6 @@ def kid_to_uuid(kid: Union[str, bytes]) -> UUID:
             kid += b"\x00" * (16 - len(kid))
 
         return UUID(bytes=kid)
+
+
+__all__ = ("Key",)
diff --git a/pywidevine/pssh.py b/pywidevine/pssh.py
index 4eb4b61..b81111a 100644
--- a/pywidevine/pssh.py
+++ b/pywidevine/pssh.py
@@ -437,3 +437,6 @@ def parse_key_ids(key_ids: list[Union[UUID, str, bytes]]) -> list[UUID]:
         ]
 
         return uuids
+
+
+__all__ = ("PSSH",)
diff --git a/pywidevine/remotecdm.py b/pywidevine/remotecdm.py
index 78e304d..7e79ce0 100644
--- a/pywidevine/remotecdm.py
+++ b/pywidevine/remotecdm.py
@@ -297,4 +297,4 @@ def get_keys(self, session_id: bytes, type_: Optional[Union[int, str]] = None) -
         ]
 
 
-__ALL__ = (RemoteCdm,)
+__all__ = ("RemoteCdm",)
diff --git a/pywidevine/session.py b/pywidevine/session.py
index 1a2744e..7cb816f 100644
--- a/pywidevine/session.py
+++ b/pywidevine/session.py
@@ -13,3 +13,6 @@ def __init__(self, number: int):
         self.service_certificate: Optional[SignedDrmCertificate] = None
         self.context: dict[bytes, tuple[bytes, bytes]] = {}
         self.keys: list[Key] = []
+
+
+__all__ = ("Session",)