diff --git a/plover/oslayer/xkeyboardcontrol.py b/plover/oslayer/xkeyboardcontrol.py
index 8177a30f4..04d76fb88 100644
--- a/plover/oslayer/xkeyboardcontrol.py
+++ b/plover/oslayer/xkeyboardcontrol.py
@@ -1172,6 +1172,7 @@ def __init__(self):
         super().start()
 
     def _on_event(self, event):
+        assert self._display_lock.locked()
         if event.type == X.MappingNotify:
             if event.request == X.MappingKeyboard:
                 if event.count == 1:
@@ -1188,11 +1189,11 @@ def _on_event(self, event):
             elif event.request == X.MappingModifier:
                 self._update_modifiers()
 
-    @with_display_lock
     def _update_keymap(self):
         '''Analyse keymap, build a mapping of keysym to (keycode + modifiers),
         and find unused keycodes that can be used for unmapped keysyms.
         '''
+        assert self._display_lock.locked() or not self.is_alive()
         self._keymap = {}
         self._custom_mappings_queue = []
         # Analyse X11 keymap.
@@ -1245,9 +1246,9 @@ def _update_keymap(self):
         assert self._backspace_mapping is not None
         assert self._backspace_mapping.custom_mapping is None
 
-    @with_display_lock
     def _update_modifiers(self):
         # Get modifier mapping.
+        assert self._display_lock.locked() or not self.is_alive()
         self.modifier_mapping = self._display.get_modifier_mapping()
 
     @with_display_lock
@@ -1372,6 +1373,7 @@ def _get_mapping(self, keysym, automatically_map=True):
         keysym -- A key symbol.
 
         """
+        assert self._display_lock.locked() or not self.is_alive()
         mapping = self._keymap.get(keysym)
         if mapping is None:
             # Automatically map?