diff --git a/lib/pathname.rb b/lib/pathname.rb
index 118666b194..423b8a0689 100644
--- a/lib/pathname.rb
+++ b/lib/pathname.rb
@@ -1141,6 +1141,25 @@ if $0 == __FILE__
       assert_equal(true,  Pathname.new("a".taint)      .to_s.tainted?)
       assert_equal(true,  Pathname.new("a".taint).taint     .tainted?)
       assert_equal(true,  Pathname.new("a".taint).taint.to_s.tainted?)
+
+      str = "a"
+      path = Pathname.new(str)
+      str.taint
+      assert_equal(false, path     .tainted?)
+      assert_equal(false, path.to_s.tainted?)
+    end
+
+    def test_untaint
+      obj = Pathname.new("a"); assert_same(obj, obj.untaint)
+
+      assert_equal(false, Pathname.new("a").taint.untaint     .tainted?)
+      assert_equal(false, Pathname.new("a").taint.untaint.to_s.tainted?)
+
+      str = "a".taint
+      path = Pathname.new(str)
+      str.untaint
+      assert_equal(true, path     .tainted?)
+      assert_equal(true, path.to_s.tainted?)
     end
 
     def test_freeze
@@ -1155,5 +1174,13 @@ if $0 == __FILE__
       assert_equal(false, Pathname.new("a"       ).freeze.to_s.frozen?)
       assert_equal(false, Pathname.new("a".freeze).freeze.to_s.frozen?)
     end
+
+    def test_to_s
+      str = "a"
+      obj = Pathname.new(str)
+      assert_equal(str, obj.to_s)
+      assert_not_same(str, obj.to_s)
+      assert_not_same(obj.to_s, obj.to_s)
+    end
   end
 end