diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 27281ad..c35f251 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -28,4 +28,4 @@ jobs:
         run: uvx ruff check --output-format=github . && uvx ruff format --check
 
       - name: Run Mypy
-        run: uvx mypy .
+        run: uv tool install ty && ty check .
diff --git a/examples/schedule.py b/examples/schedule.py
index 8061fa4..ea56ec9 100644
--- a/examples/schedule.py
+++ b/examples/schedule.py
@@ -39,7 +39,8 @@ def schedule_new_card():
     card.memory_state = next_state.memory
     card.scheduled_days = interval
     card.last_review = datetime.datetime.now(datetime.timezone.utc)
-    card.due = card.last_review + datetime.timedelta(days=interval)
+    if card.last_review is not None:  # make ty happy
+        card.due = card.last_review + datetime.timedelta(days=interval)
 
     print(f"Next review due: {card.due}")
     print(f"Memory state: {card.memory_state}")
@@ -79,7 +80,8 @@ def schedule_existing_card():
     card.memory_state = next_state.memory
     card.scheduled_days = interval
     card.last_review = datetime.datetime.now(datetime.timezone.utc)
-    card.due = card.last_review + datetime.timedelta(days=interval)
+    if card.last_review is not None:  # make ty happy
+        card.due = card.last_review + datetime.timedelta(days=interval)
 
     print(f"Next review due: {card.due}")
     print(f"Memory state: {card.memory_state}")