diff --git a/litellm/proxy/management_endpoints/customer_endpoints.py b/litellm/proxy/management_endpoints/customer_endpoints.py
index 388888d960d..4127bc973e4 100644
--- a/litellm/proxy/management_endpoints/customer_endpoints.py
+++ b/litellm/proxy/management_endpoints/customer_endpoints.py
@@ -553,7 +553,10 @@ async def update_end_user(
         # get non default values for key
         non_default_values = {}
         for k, v in data_json.items():
-            if v is not None and (isinstance(v, bool) or v not in ([], {}, 0)):
+            if v is not None and (
+                (isinstance(v, bool) and k in data.fields_set())
+                or v not in ([], {}, 0)
+            ):
                 non_default_values[k] = v
 
         ## Get end user table data ##
diff --git a/tests/test_litellm/proxy/management_endpoints/test_customer_endpoints.py b/tests/test_litellm/proxy/management_endpoints/test_customer_endpoints.py
index c1479d4539c..6eb03256b67 100644
--- a/tests/test_litellm/proxy/management_endpoints/test_customer_endpoints.py
+++ b/tests/test_litellm/proxy/management_endpoints/test_customer_endpoints.py
@@ -105,6 +105,30 @@ def test_update_customer_unblock(mock_prisma_client, mock_user_api_key_auth):
     assert update_mock.call_args.kwargs["data"]["blocked"] is False
 
 
+def test_update_customer_keeps_blocked_when_omitted(mock_prisma_client, mock_user_api_key_auth):
+    """
+    Regression test: updating a blocked customer without supplying `blocked`
+    must NOT reset it to unblocked. `blocked=False` is the model default and
+    should only be applied when explicitly provided by the caller.
+    """
+    mock_end_user = LiteLLM_EndUserTable(user_id="test-user-1", blocked=True)
+    updated_mock_end_user = LiteLLM_EndUserTable(user_id="test-user-1", blocked=True)
+
+    mock_prisma_client.db.litellm_endusertable.find_first = AsyncMock(return_value=mock_end_user)
+    mock_prisma_client.db.litellm_endusertable.update = AsyncMock(return_value=updated_mock_end_user)
+
+    response = client.post(
+        "/customer/update",
+        json={"user_id": "test-user-1", "alias": "Updated Test User"},
+        headers={"Authorization": "Bearer test-key"},
+    )
+
+    assert response.status_code == 200
+    update_mock = mock_prisma_client.db.litellm_endusertable.update
+    update_mock.assert_called_once()
+    assert "blocked" not in update_mock.call_args.kwargs["data"]
+
+
 def test_update_customer_not_found(mock_prisma_client, mock_user_api_key_auth):
     """
     Test that update_end_user raises a 404 ProxyException when user_id does not exist.