diff --git a/.mypy.ini b/.mypy.ini
index 30db8f069..325b624d0 100644
--- a/.mypy.ini
+++ b/.mypy.ini
@@ -46,6 +46,8 @@ strict_optional = True
 strict_optional = True
 [mypy-aqt.overview]
 strict_optional = True
+[mypy-aqt.customstudy]
+strict_optional = True
 [mypy-anki.scheduler.base]
 strict_optional = True
 [mypy-anki._backend.rsbridge]
diff --git a/qt/aqt/customstudy.py b/qt/aqt/customstudy.py
index 730f3843b..eb8921627 100644
--- a/qt/aqt/customstudy.py
+++ b/qt/aqt/customstudy.py
@@ -144,7 +144,11 @@ class CustomStudy(QDialog):
         form.spin.setValue(current_spinner_value)
         form.preSpin.setText(text_before_spinner)
         form.postSpin.setText(text_after_spinner)
-        form.buttonBox.button(QDialogButtonBox.StandardButton.Ok).setText(ok)
+
+        ok_button = form.buttonBox.button(QDialogButtonBox.StandardButton.Ok)
+        assert ok_button is not None
+        ok_button.setText(ok)
+
         self.radioIdx = idx
 
     def accept(self) -> None: