diff --git a/gc.c b/gc.c
index d9c873166f..fcb9c6454e 100644
--- a/gc.c
+++ b/gc.c
@@ -7347,15 +7347,19 @@ rb_gc_force_recycle(VALUE obj)
 void
 rb_gc_register_mark_object(VALUE obj)
 {
-    VALUE ary_ary = GET_VM()->mark_object_ary;
-    VALUE ary = rb_ary_last(0, 0, ary_ary);
+    RB_VM_LOCK_ENTER();
+    {
+        VALUE ary_ary = GET_VM()->mark_object_ary;
+        VALUE ary = rb_ary_last(0, 0, ary_ary);
 
-    if (ary == Qnil || RARRAY_LEN(ary) >= MARK_OBJECT_ARY_BUCKET_SIZE) {
-	ary = rb_ary_tmp_new(MARK_OBJECT_ARY_BUCKET_SIZE);
-	rb_ary_push(ary_ary, ary);
+        if (ary == Qnil || RARRAY_LEN(ary) >= MARK_OBJECT_ARY_BUCKET_SIZE) {
+            ary = rb_ary_tmp_new(MARK_OBJECT_ARY_BUCKET_SIZE);
+            rb_ary_push(ary_ary, ary);
+        }
+
+        rb_ary_push(ary, obj);
     }
-
-    rb_ary_push(ary, obj);
+    RB_VM_LOCK_LEAVE();
 }
 
 void