diff --git a/ChangeLog b/ChangeLog
index 0d8eccd168..8591c4ef81 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Fri Dec 13 12:01:07 2013  Koichi Sasada  <ko1@atdot.net>
+
+	* gc.c (garbage_collect_body): use rb_bug() and explicit error message
+	  instead of using assert().
+	  [Bug #9222]
+
 Fri Dec 13 11:52:41 2013  Koichi Sasada  <ko1@atdot.net>
 
 	* array.c: fix comment to remove the word "shady".
diff --git a/gc.c b/gc.c
index d74056bbb2..5eb60e1e96 100644
--- a/gc.c
+++ b/gc.c
@@ -4940,6 +4940,7 @@ garbage_collect_body(rb_objspace_t *objspace, int full_mark, int immediate_sweep
 
     objspace->profile.count++;
     objspace->profile.latest_gc_info = reason;
+
     gc_event_hook(objspace, RUBY_INTERNAL_EVENT_GC_START, 0 /* TODO: pass minor/immediate flag? */);
 
     objspace->profile.total_allocated_object_num_at_gc_start = objspace->profile.total_allocated_object_num;
@@ -4948,7 +4949,9 @@ garbage_collect_body(rb_objspace_t *objspace, int full_mark, int immediate_sweep
     gc_prof_setup_new_record(objspace, reason);
     gc_prof_timer_start(objspace);
     {
-	assert(during_gc > 0);
+	if (during_gc == 0) {
+	    rb_bug("during_gc should not be 0. RUBY_INTERNAL_EVENT_GC_START user should not cause GC in events.");
+	}
 	gc_marks(objspace, full_mark);
 	gc_sweep(objspace, immediate_sweep);
 	during_gc = 0;