diff --git a/thread.c b/thread.c
index 4022f60..98ad9af 100644
--- a/thread.c
+++ b/thread.c
@@ -3933,6 +3933,7 @@ set_trace_func(VALUE obj, VALUE trace)
     rb_remove_event_hook(call_trace_func);
 
     if (NIL_P(trace)) {
+	GET_THREAD()->tracing = 0;
 	return Qnil;
     }
 
@@ -3989,6 +3990,7 @@ thread_set_trace_func_m(VALUE obj, VALUE trace)
     rb_threadptr_revmove_event_hook(th, call_trace_func);
 
     if (NIL_P(trace)) {
+	th->tracing = 0;
 	return Qnil;
     }
     thread_add_trace_func(th, trace);