diff --git a/litellm/integrations/rubrik.py b/litellm/integrations/rubrik.py
index 601a1376cb3..485389b8b39 100644
--- a/litellm/integrations/rubrik.py
+++ b/litellm/integrations/rubrik.py
@@ -48,11 +48,15 @@ class RubrikLogger(CustomGuardrail, CustomBatchLogger):
     ):
         self.flush_lock = asyncio.Lock()
         kwargs.setdefault("guardrail_name", "rubrik")
-        # Use `or` rather than setdefault because callers (e.g.
-        # initialize_guardrail) always pass event_hook explicitly, possibly as
-        # None when the user omits `mode` from the guardrail config.
+        # `initialize_guardrail` always passes these kwargs explicitly, with
+        # value `None` when the user omits `mode` / `default_on` from the
+        # guardrail config. Coerce None (omitted) to the desired default
+        # while preserving any explicit value the caller did set --
+        # in particular `default_on=False` if the user wants the guardrail
+        # off by default.
         kwargs["event_hook"] = kwargs.get("event_hook") or GuardrailEventHooks.post_call
-        kwargs.setdefault("default_on", True)
+        if kwargs.get("default_on") is None:
+            kwargs["default_on"] = True
         super().__init__(
             flush_lock=self.flush_lock,
             **kwargs,
diff --git a/tests/test_litellm/integrations/test_rubrik.py b/tests/test_litellm/integrations/test_rubrik.py
index 113868480c5..56799641d90 100644
--- a/tests/test_litellm/integrations/test_rubrik.py
+++ b/tests/test_litellm/integrations/test_rubrik.py
@@ -204,6 +204,27 @@ class TestInitialization:
             handler = RubrikLogger(event_hook=GuardrailEventHooks.pre_call)
             assert handler.event_hook == GuardrailEventHooks.pre_call
 
+    def test_default_on_defaults_to_true_when_none_passed(self, mock_env):
+        """`initialize_guardrail` always passes ``default_on=litellm_params.default_on``
+        (which is ``None`` when the user omits ``default_on``). The logger must
+        coerce a None ``default_on`` to True, otherwise ``should_run_guardrail``
+        (which checks ``self.default_on is True``) silently skips the guardrail."""
+        with patch("asyncio.create_task", Mock()):
+            handler = RubrikLogger(default_on=None)
+            assert handler.default_on is True
+
+    def test_explicit_default_on_false_preserved(self, mock_env):
+        """A user explicitly setting ``default_on: false`` in their guardrail
+        config must NOT be silently overridden to True."""
+        with patch("asyncio.create_task", Mock()):
+            handler = RubrikLogger(default_on=False)
+            assert handler.default_on is False
+
+    def test_explicit_default_on_true_preserved(self, mock_env):
+        with patch("asyncio.create_task", Mock()):
+            handler = RubrikLogger(default_on=True)
+            assert handler.default_on is True
+
     def test_headers_with_api_key(self, handler):
         assert handler._headers["Authorization"] == "Bearer test-api-key"
         assert handler._headers["Content-Type"] == "application/json"