diff --git a/backend/magic_plan/tests/test_magic_plan_client.py b/backend/magic_plan/tests/test_magic_plan_client.py
index c96b9cdf..cb2385b1 100644
--- a/backend/magic_plan/tests/test_magic_plan_client.py
+++ b/backend/magic_plan/tests/test_magic_plan_client.py
@@ -20,6 +20,7 @@ def _load_fixture(name: str) -> dict[str, Any]:
 
 
 def _make_client(mock_session: MagicMock) -> MagicPlanClient:
+    mock_session.headers = {}
     with patch(
         "backend.magic_plan.magic_plan_client.requests.Session",
         return_value=mock_session,
@@ -44,7 +45,14 @@ def test_customer_header_set_on_session(mock_session: MagicMock) -> None:
     # Act
     _make_client(mock_session)
     # Assert
-    mock_session.headers.update.assert_called_once_with({"customer": CUSTOMER_ID})
+    assert mock_session.headers["customer"] == CUSTOMER_ID
+
+
+def test_api_key_header_set_on_session(mock_session: MagicMock) -> None:
+    # Act
+    _make_client(mock_session)
+    # Assert
+    assert mock_session.headers["key"] == API_KEY
 
 
 # --- get_plans ---