diff --git a/pywidevine/cdm.py b/pywidevine/cdm.py
index 08dcfc0..eab5231 100644
--- a/pywidevine/cdm.py
+++ b/pywidevine/cdm.py
@@ -131,7 +131,7 @@ class Cdm:
         if len(self.__sessions) > self.MAX_NUM_OF_SESSIONS:
             raise TooManySessions(f"Too many Sessions open ({self.MAX_NUM_OF_SESSIONS}).")
 
-        session = Session()
+        session = Session(len(self.__sessions) + 1)
         self.__sessions[session.id] = session
 
         return session.id
diff --git a/pywidevine/session.py b/pywidevine/session.py
index cc123df..2bfcdaf 100644
--- a/pywidevine/session.py
+++ b/pywidevine/session.py
@@ -7,7 +7,8 @@ from pywidevine.license_protocol_pb2 import SignedMessage
 
 
 class Session:
-    def __init__(self):
+    def __init__(self, number: int):
+        self.number = number
         self.id = get_random_bytes(16)
         self.service_certificate: Optional[SignedMessage] = None
         self.context: dict[bytes, tuple[bytes, bytes]] = {}