diff --git a/test/-ext-/symbol/test_type.rb b/test/-ext-/symbol/test_type.rb
index 3c21e61a18..ddd79561ab 100644
--- a/test/-ext-/symbol/test_type.rb
+++ b/test/-ext-/symbol/test_type.rb
@@ -122,17 +122,21 @@ module Test_Symbol
     end
 
     def test_check_id_invalid_type
-      cx = EnvUtil.labeled_class("X\u{1f431}")
-      assert_raise_with_message(TypeError, /X\u{1F431}/) {
-        Bug::Symbol.pinneddown?(cx)
-      }
+      EnvUtil.with_default_external(Encoding::UTF_8) do
+        cx = EnvUtil.labeled_class("X\u{1f431}")
+        assert_raise_with_message(TypeError, /X\u{1F431}/) {
+          Bug::Symbol.pinneddown?(cx)
+        }
+      end
     end
 
     def test_check_symbol_invalid_type
-      cx = EnvUtil.labeled_class("X\u{1f431}")
-      assert_raise_with_message(TypeError, /X\u{1F431}/) {
-        Bug::Symbol.find(cx)
-      }
+      EnvUtil.with_default_external(Encoding::UTF_8) do
+        cx = EnvUtil.labeled_class("X\u{1f431}")
+        assert_raise_with_message(TypeError, /X\u{1F431}/) {
+          Bug::Symbol.find(cx)
+        }
+      end
     end
   end
 end
diff --git a/test/ruby/test_method.rb b/test/ruby/test_method.rb
index ac92729f0a..b7b140d9a0 100644
--- a/test/ruby/test_method.rb
+++ b/test/ruby/test_method.rb
@@ -251,10 +251,12 @@ class TestMethod < Test::Unit::TestCase
     m = o.method(:bar).unbind
     assert_raise(TypeError) { m.bind(Object.new) }
 
-    cx = EnvUtil.labeled_class("X\u{1f431}")
-    assert_raise_with_message(TypeError, /X\u{1f431}/) {
-      o.method(cx)
-    }
+    EnvUtil.with_default_external(Encoding::UTF_8) do
+      cx = EnvUtil.labeled_class("X\u{1f431}")
+      assert_raise_with_message(TypeError, /X\u{1f431}/) {
+        o.method(cx)
+      }
+    end
   end
 
   def test_bind_module_instance_method
@@ -283,10 +285,12 @@ class TestMethod < Test::Unit::TestCase
     assert_raise(TypeError) do
       Class.new.class_eval { define_method(:bar, o.method(:bar)) }
     end
-    cx = EnvUtil.labeled_class("X\u{1f431}")
-    assert_raise_with_message(TypeError, /X\u{1F431}/) {
-      Class.new {define_method(cx) {}}
-    }
+    EnvUtil.with_default_external(Encoding::UTF_8) do
+      cx = EnvUtil.labeled_class("X\u{1f431}")
+      assert_raise_with_message(TypeError, /X\u{1F431}/) {
+        Class.new {define_method(cx) {}}
+      }
+    end
   end
 
   def test_define_method_no_proc