diff --git a/ext/bigdecimal/extconf.rb b/ext/bigdecimal/extconf.rb
index 0fcc7c90..47f26381 100644
--- a/ext/bigdecimal/extconf.rb
+++ b/ext/bigdecimal/extconf.rb
@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require 'mkmf'
 
 def have_builtin_func(name, check_expr, opt = "", &b)
diff --git a/lib/bigdecimal/math.rb b/lib/bigdecimal/math.rb
index a8534aa1..9dff366d 100644
--- a/lib/bigdecimal/math.rb
+++ b/lib/bigdecimal/math.rb
@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require 'bigdecimal'
 
 #
diff --git a/lib/bigdecimal/util.rb b/lib/bigdecimal/util.rb
index 7c5f32eb..7f2232db 100644
--- a/lib/bigdecimal/util.rb
+++ b/lib/bigdecimal/util.rb
@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 #
 #--
 # bigdecimal/util extends various native classes to provide the #to_d method,
diff --git a/sample/linear.rb b/sample/linear.rb
index 6cc72e25..0cfac03e 100644
--- a/sample/linear.rb
+++ b/sample/linear.rb
@@ -1,5 +1,3 @@
-# frozen_string_literal: false
-
 #
 # linear.rb
 #
diff --git a/sample/nlsolve.rb b/sample/nlsolve.rb
index 1e63578b..79536533 100644
--- a/sample/nlsolve.rb
+++ b/sample/nlsolve.rb
@@ -1,5 +1,3 @@
-# frozen_string_literal: false
-
 #
 # nlsolve.rb
 # An example for solving nonlinear algebraic equation system.
diff --git a/sample/pi.rb b/sample/pi.rb
index 3315d333..0dc27c43 100644
--- a/sample/pi.rb
+++ b/sample/pi.rb
@@ -1,5 +1,3 @@
-# frozen_string_literal: false
-
 #
 # pi.rb
 #
diff --git a/test/bigdecimal/helper.rb b/test/bigdecimal/helper.rb
index 37089bd8..f624edf8 100644
--- a/test/bigdecimal/helper.rb
+++ b/test/bigdecimal/helper.rb
@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require "test/unit"
 require "bigdecimal"
 require 'rbconfig/sizeof'
diff --git a/test/bigdecimal/test_bigdecimal.rb b/test/bigdecimal/test_bigdecimal.rb
index aff7a2f2..03f7f2ae 100644
--- a/test/bigdecimal/test_bigdecimal.rb
+++ b/test/bigdecimal/test_bigdecimal.rb
@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require_relative "helper"
 require 'bigdecimal/math'
 
@@ -266,7 +266,7 @@ def test_BigDecimal_with_big_decimal
     def test_BigDecimal_with_tainted_string
       Thread.new {
         $SAFE = 1
-        BigDecimal('1'.taint)
+        BigDecimal('1'.dup.taint)
       }.join
     ensure
       $SAFE = 0
diff --git a/test/bigdecimal/test_bigdecimal_util.rb b/test/bigdecimal/test_bigdecimal_util.rb
index 19790287..34c46bc9 100644
--- a/test/bigdecimal/test_bigdecimal_util.rb
+++ b/test/bigdecimal/test_bigdecimal_util.rb
@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require_relative "helper"
 require 'bigdecimal/util'
 
diff --git a/test/bigdecimal/test_bigmath.rb b/test/bigdecimal/test_bigmath.rb
index 903fd7f9..5a6f4ee0 100644
--- a/test/bigdecimal/test_bigmath.rb
+++ b/test/bigdecimal/test_bigmath.rb
@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require_relative "helper"
 require "bigdecimal/math"
 
diff --git a/test/bigdecimal/test_jruby.rb b/test/bigdecimal/test_jruby.rb
index e02cbf08..5886b245 100644
--- a/test/bigdecimal/test_jruby.rb
+++ b/test/bigdecimal/test_jruby.rb
@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require_relative 'helper'
 require 'bigdecimal/math'
 
diff --git a/test/bigdecimal/test_vp_operation.rb b/test/bigdecimal/test_vp_operation.rb
index 075df0b6..b2f1d75a 100644
--- a/test/bigdecimal/test_vp_operation.rb
+++ b/test/bigdecimal/test_vp_operation.rb
@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require_relative 'helper'
 require 'bigdecimal'