diff --git a/src/aare/gui/main_window.py b/src/aare/gui/main_window.py
index 471b342a..40b98ec4 100644
--- a/src/aare/gui/main_window.py
+++ b/src/aare/gui/main_window.py
@@ -1631,7 +1631,10 @@ class MainWindow(QMainWindow):
                 if view.isVisible():
                     view.update_pixmap(pixmap)
         finally:
-            self.prediction_thread.notify_frame_displayed()
+            # The slot is only connected once the subscriber exists, but the
+            # attribute is Optional so the guard is what the type checker needs.
+            if self.prediction_thread is not None:
+                self.prediction_thread.notify_frame_displayed()
 
     @Slot(bool)
     def _on_sample_camera_availability_changed(self, available: bool) -> None:
diff --git a/src/aare/gui/threads/prediction_subscriber.py b/src/aare/gui/threads/prediction_subscriber.py
index 1def221c..e5c40980 100644
--- a/src/aare/gui/threads/prediction_subscriber.py
+++ b/src/aare/gui/threads/prediction_subscriber.py
@@ -201,10 +201,14 @@ class PredictionSubscriber(QThread):
         backlog that piled up while we were busy, and the stream is always
         consumed at line rate no matter how long a frame takes to decode.
         """
-        parts = self._sock.recv_multipart()  # honours RCVTIMEO, may raise zmq.Again
+        # Bind locally: run() nulls the attribute on cleanup, so it is Optional
+        # to the type checker even though it cannot be None while run() loops.
+        sock = self._sock
+        assert sock is not None, "_recv_latest called after the socket was closed"
+        parts = sock.recv_multipart()  # honours RCVTIMEO, may raise zmq.Again
         while True:
             try:
-                parts = self._sock.recv_multipart(zmq.NOBLOCK)
+                parts = sock.recv_multipart(zmq.NOBLOCK)
             except zmq.Again:
                 return parts
             self._dropped += 1