diff --git a/nostr/subscription.py b/nostr/subscription.py
index 7afba20..37829c1 100644
--- a/nostr/subscription.py
+++ b/nostr/subscription.py
@@ -1,7 +1,9 @@
 from .filter import Filters
 
 class Subscription:
-    def __init__(self, id: str, filters: Filters=None) -> None:
+    def __init__(self, id: str, filters: Filters) -> None:
+        if not isinstance(id, str):
+            raise TypeError("Argument 'id' must be of type str")
         self.id = id
         self.filters = filters
 
diff --git a/test/test_subscription.py b/test/test_subscription.py
new file mode 100644
index 0000000..dbb0893
--- /dev/null
+++ b/test/test_subscription.py
@@ -0,0 +1,28 @@
+import pytest
+import json
+from nostr.filter import Filter, Filters
+from nostr.message_type import ClientMessageType
+from nostr.subscription import Subscription
+
+
+def test_subscription_id():
+    """
+        check that subscription contents dump to JSON and load
+        back to Python with expected types
+    """
+    filters = Filters([Filter()])
+    id = 123
+    
+    with pytest.raises(TypeError) as e:
+        subscription = Subscription(id=id, filters=filters)
+    assert "Argument 'id' must be of type str" == str(e)
+
+    subscription = Subscription(id=str(id), filters=filters)
+    request = [ClientMessageType.REQUEST, subscription.id]
+    request.extend(subscription.filters.to_json_array())
+    message = json.dumps(request)
+    request_received = json.loads(message)
+    message_type, subscription_id, req_filters = request_received
+    assert isinstance(subscription_id, str)
+    assert message_type == ClientMessageType.REQUEST
+    assert isinstance(req_filters, dict)