diff --git a/test/ruby/test_gc_compact.rb b/test/ruby/test_gc_compact.rb
index 0c49b36513..e11b34707f 100644
--- a/test/ruby/test_gc_compact.rb
+++ b/test/ruby/test_gc_compact.rb
@@ -353,7 +353,7 @@ class TestGCCompact < Test::Unit::TestCase
   def test_moving_objects_between_size_pools
     omit if GC::INTERNAL_CONSTANTS[:SIZE_POOL_COUNT] == 1
 
-    assert_separately([], "#{<<~"begin;"}\n#{<<~"end;"}", timeout: 10, signal: :SEGV)
+    assert_separately(%w[-robjspace], "#{<<~"begin;"}\n#{<<~"end;"}", timeout: 10, signal: :SEGV)
     begin;
       class Foo
         def add_ivars
@@ -376,6 +376,7 @@ class TestGCCompact < Test::Unit::TestCase
       stats = GC.verify_compaction_references(expand_heap: true, toward: :empty)
 
       assert_operator(stats.dig(:moved_up, :T_OBJECT) || 0, :>=, OBJ_COUNT)
+      assert_include(ObjectSpace.dump(ary[0]), '"embedded":true')
     end;
   end