I think I found why it crashes I add another printf in event_stream_disable_wakeup like this one-shot. */ if (!NILP (rest)) { Lisp_Object op = XCAR (rest); *timeout_list = delq_no_quit_and_free_cons (op, *timeout_list); fprintf(stderr,"Unlist %i\n",timeout->interval_id); if (async_p) event_stream_remove_async_timeout (timeout->interval_id); else event_stream_remove_timeout (timeout->interval_id); free_managed_opaque (Vtimeout_free_list, op); (Note: For me it safer to delete the timer first and then delete it from the list). Now look at the trace Unlist 73 Removed: 4377440 Allocated: 82 InList 82 Completed: 82 Looking up: 82 (0) Allocated: 83 Unlist 83 Removed: 4377440 Up to here evey "UnList" if followed by an Removed call Allocated: 84 InList 84 Unlist 84 Here it isn't! Allocated: 85 InList 85 Unlist 85 Removed: 4377440 Allocated: 86 InList 86 Completed: 84 Looking up: 84 (0) Fatal error: assertion failed, file event-stream.c, line 1214, !NILP (rest) And now "84" comes in and BOOM! Now you tell me what this has to do with drag and drop... Jan