diff --git a/superxas_bec/devices/timepix/timepix.py b/superxas_bec/devices/timepix/timepix.py
index ef38649..abce52a 100644
--- a/superxas_bec/devices/timepix/timepix.py
+++ b/superxas_bec/devices/timepix/timepix.py
@@ -76,7 +76,8 @@ class AndStatus(StatusBase):
                     self.set_finished()
 
         for st in self.all_statuses:
-            st.add_callback(inner)
+            with st._lock:
+                st.add_callback(inner)
 
     def __repr__(self):
         return "({self.left!r} & {self.right!r})".format(self=self)