1 files changed, 5 insertions, 5 deletions
diff --git a/spec/ruby/core/string/bytesize_spec.rb b/spec/ruby/core/string/bytesize_spec.rb
index a31f3ae671..2bbefc0820 100644
--- a/spec/ruby/core/string/bytesize_spec.rb
+++ b/spec/ruby/core/string/bytesize_spec.rb
@@ -13,21 +13,21 @@ describe "String#bytesize" do
   end
 
   it "works with pseudo-ASCII strings containing single UTF-8 characters" do
-    "\u{6666}".force_encoding('ASCII').bytesize.should == 3
+    "\u{6666}".dup.force_encoding('ASCII').bytesize.should == 3
   end
 
   it "works with strings containing UTF-8 characters" do
-    "c \u{6666}".force_encoding('UTF-8').bytesize.should == 5
+    "c \u{6666}".dup.force_encoding('UTF-8').bytesize.should == 5
     "c \u{6666}".bytesize.should == 5
   end
 
   it "works with pseudo-ASCII strings containing UTF-8 characters" do
-    "c \u{6666}".force_encoding('ASCII').bytesize.should == 5
+    "c \u{6666}".dup.force_encoding('ASCII').bytesize.should == 5
   end
 
   it "returns 0 for the empty string" do
     "".bytesize.should == 0
-    "".force_encoding('ASCII').bytesize.should == 0
-    "".force_encoding('UTF-8').bytesize.should == 0
+    "".dup.force_encoding('ASCII').bytesize.should == 0
+    "".dup.force_encoding('UTF-8').bytesize.should == 0
   end
 end