diff --git a/Xi/exevents.c b/Xi/exevents.c
index 815eb7c6c..1d4dc51bf 100644
--- a/Xi/exevents.c
+++ b/Xi/exevents.c
@@ -434,6 +434,7 @@ DeepCopyDeviceClasses(DeviceIntPtr from, DeviceIntPtr to)
 #ifdef XKB
         to->key->xkbInfo = NULL;
 #endif
+        to->key->modifierKeyMap = NULL;
         to->key->curKeySyms.map = NULL;
         CopyKeyClass(from, to);
     } else if (to->key && !from->key)