diff --git a/litellm/proxy/guardrails/guardrail_hooks/presidio.py b/litellm/proxy/guardrails/guardrail_hooks/presidio.py
index 3d2ab334402..e749b167c75 100644
--- a/litellm/proxy/guardrails/guardrail_hooks/presidio.py
+++ b/litellm/proxy/guardrails/guardrail_hooks/presidio.py
@@ -106,8 +106,8 @@ class _OPTIONAL_PresidioPIIMasking(CustomGuardrail):
         # so should_run_guardrail returns True for both pre_call and post_call.
         if (self.output_parse_pii or self.apply_to_output) and not logging_only:
             current_hook = self.event_hook
-            if isinstance(current_hook, str) and current_hook == "pre_call":
-                self.event_hook = ["pre_call", "post_call"]
+            if isinstance(current_hook, str) and current_hook != "post_call":
+                self.event_hook = [current_hook, "post_call"]
             elif isinstance(current_hook, list) and "post_call" not in current_hook:
                 self.event_hook = current_hook + ["post_call"]
         self.pii_entities_config: Dict[Union[PiiEntityType, str], PiiAction] = (
diff --git a/tests/test_litellm/proxy/guardrails/guardrail_hooks/test_presidio.py b/tests/test_litellm/proxy/guardrails/guardrail_hooks/test_presidio.py
index e336f2f1bf8..55137176a60 100644
--- a/tests/test_litellm/proxy/guardrails/guardrail_hooks/test_presidio.py
+++ b/tests/test_litellm/proxy/guardrails/guardrail_hooks/test_presidio.py
@@ -1711,3 +1711,34 @@ async def test_pii_tokens_in_metadata_used_for_unmasking():
     )
 
     assert response.choices[0].message.content == "Hello John, how can I help you?"
+
+
+@pytest.mark.parametrize(
+    "initial_hook",
+    ["pre_call", "during_call", "pre_mcp_call"],
+)
+def test_event_hook_auto_expansion_for_all_string_hooks(initial_hook):
+    """
+    Regression test: when output_parse_pii is True, the guardrail must add
+    'post_call' to event_hook regardless of the initial string hook value,
+    not just when it's 'pre_call'.
+    """
+    guardrail = _OPTIONAL_PresidioPIIMasking(
+        mock_testing=True,
+        output_parse_pii=True,
+        event_hook=initial_hook,
+    )
+    assert isinstance(guardrail.event_hook, list)
+    assert initial_hook in guardrail.event_hook
+    assert "post_call" in guardrail.event_hook
+
+
+def test_event_hook_no_expansion_when_already_post_call():
+    """post_call alone should stay as-is — no expansion needed."""
+    guardrail = _OPTIONAL_PresidioPIIMasking(
+        mock_testing=True,
+        output_parse_pii=True,
+        event_hook="post_call",
+    )
+    # Should remain a string "post_call", not expanded to a list
+    assert guardrail.event_hook == "post_call"