diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 22898000..e1e72aa2 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -8,7 +8,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu]
-        ruby: ['2.4', '2.5', '2.6', '2.7', '3.0', '3.1', jruby, truffleruby]
+        ruby: ['2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', jruby, truffleruby]
         include:
           - os: macos
             ruby: '2.4'
@@ -31,12 +31,36 @@ jobs:
         FULL_ZIP64_TEST: 1
       run: bundle exec rake
 
+  test-frozen-string-literal:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu]
+        ruby: ['3.3']
+    runs-on: ${{ matrix.os }}-latest
+    continue-on-error: true
+    steps:
+    - name: Checkout rubyzip code
+      uses: actions/checkout@v2
+
+    - name: Install and set up ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
+
+    - name: Run the tests
+      env:
+        RUBYOPT: --enable-frozen-string-literal
+        FULL_ZIP64_TEST: 1
+      run: bundle exec rake
+
   test-yjit:
     strategy:
       fail-fast: false
       matrix:
         os: [ubuntu, macos]
-        ruby: ['3.1', head]
+        ruby: ['3.1', '3.2', '3.3', head]
     runs-on: ${{ matrix.os }}-latest
     continue-on-error: true
     steps:
diff --git a/README.md b/README.md
index 9fe2ba68..38cb3cb3 100644
--- a/README.md
+++ b/README.md
@@ -188,7 +188,7 @@ If `::Zip::InputStream` finds such entry in the zip archive it will raise an exc
 Rubyzip supports reading/writing zip files with traditional zip encryption (a.k.a. "ZipCrypto"). AES encryption is not yet supported. It can be used with buffer streams, e.g.:
 
 ```ruby
-Zip::OutputStream.write_buffer(::StringIO.new(''), Zip::TraditionalEncrypter.new('password')) do |out|
+Zip::OutputStream.write_buffer(::StringIO.new, Zip::TraditionalEncrypter.new('password')) do |out|
   out.put_next_entry("my_file.txt")
   out.write my_data
 end.string
diff --git a/lib/zip/extra_field/zip64.rb b/lib/zip/extra_field/zip64.rb
index 9826c6cf..93bf7abd 100644
--- a/lib/zip/extra_field/zip64.rb
+++ b/lib/zip/extra_field/zip64.rb
@@ -59,7 +59,7 @@ def pack_for_local
 
     def pack_for_c_dir
       # central directory entries contain only fields that didn't fit in the main entry part
-      packed = ''.force_encoding('BINARY')
+      packed = ''.b
       packed << [@original_size].pack('Q<') if @original_size
       packed << [@compressed_size].pack('Q<') if @compressed_size
       packed << [@relative_header_offset].pack('Q<') if @relative_header_offset
diff --git a/lib/zip/file.rb b/lib/zip/file.rb
index fbbf17c9..256f052e 100644
--- a/lib/zip/file.rb
+++ b/lib/zip/file.rb
@@ -140,7 +140,7 @@ def open(file_name, dep_create = false, create: false, **options)
       def add_buffer
         Zip.warn_about_v3_api('Zip::File.add_buffer')
 
-        io = ::StringIO.new('')
+        io = ::StringIO.new
         zf = ::Zip::File.new(io, true, true)
         yield zf
         zf.write_buffer(io)
@@ -411,7 +411,7 @@ def commit
     end
 
     # Write buffer write changes to buffer and return
-    def write_buffer(io = ::StringIO.new(''))
+    def write_buffer(io = ::StringIO.new)
       return unless commit_required?
 
       ::Zip::OutputStream.write_buffer(io) do |zos|
diff --git a/lib/zip/filesystem.rb b/lib/zip/filesystem.rb
index d9928d4a..77655c6e 100644
--- a/lib/zip/filesystem.rb
+++ b/lib/zip/filesystem.rb
@@ -239,7 +239,7 @@ def directory?(filename)
       end
 
       def open(filename, mode = 'r', permissions = 0o644, &block)
-        mode.delete!('b') # ignore b option
+        mode = mode.delete('b') # ignore b option
         case mode
         when 'r'
           @mapped_zip.get_input_stream(filename, &block)
@@ -619,7 +619,7 @@ def each
       end
 
       def expand_path(path)
-        expanded = path.start_with?('/') ? path : ::File.join(@pwd, path)
+        expanded = path.start_with?('/') ? path.dup : ::File.join(@pwd, path)
         expanded.gsub!(/\/\.(\/|$)/, '')
         expanded.gsub!(/[^\/]+\/\.\.(\/|$)/, '')
         expanded.empty? ? '/' : expanded
diff --git a/lib/zip/inflater.rb b/lib/zip/inflater.rb
index 530f98aa..31627ebb 100644
--- a/lib/zip/inflater.rb
+++ b/lib/zip/inflater.rb
@@ -3,11 +3,11 @@ class Inflater < Decompressor #:nodoc:all
     def initialize(*args)
       super
 
-      @buffer = +''
+      @buffer = ''.b
       @zlib_inflater = ::Zlib::Inflate.new(-Zlib::MAX_WBITS)
     end
 
-    def read(length = nil, outbuf = '')
+    def read(length = nil, outbuf = ''.b)
       return (length.nil? || length.zero? ? '' : nil) if eof
 
       while length.nil? || (@buffer.bytesize < length)
diff --git a/lib/zip/ioextras.rb b/lib/zip/ioextras.rb
index 63774d33..6748776d 100644
--- a/lib/zip/ioextras.rb
+++ b/lib/zip/ioextras.rb
@@ -6,14 +6,14 @@ module IOExtras #:nodoc:
 
     class << self
       def copy_stream(ostream, istream)
-        ostream.write(istream.read(CHUNK_SIZE, '')) until istream.eof?
+        ostream.write(istream.read(CHUNK_SIZE, ''.b)) until istream.eof?
       end
 
       def copy_stream_n(ostream, istream, nbytes)
         toread = nbytes
         while toread > 0 && !istream.eof?
           tr = toread > CHUNK_SIZE ? CHUNK_SIZE : toread
-          ostream.write(istream.read(tr, ''))
+          ostream.write(istream.read(tr, ''.b))
           toread -= tr
         end
       end
diff --git a/lib/zip/ioextras/abstract_input_stream.rb b/lib/zip/ioextras/abstract_input_stream.rb
index 8392d240..dc239d67 100644
--- a/lib/zip/ioextras/abstract_input_stream.rb
+++ b/lib/zip/ioextras/abstract_input_stream.rb
@@ -11,13 +11,13 @@ def initialize
         super
         @lineno        = 0
         @pos           = 0
-        @output_buffer = ''
+        @output_buffer = ''.b
       end
 
       attr_accessor :lineno
       attr_reader :pos
 
-      def read(number_of_bytes = nil, buf = '')
+      def read(number_of_bytes = nil, buf = ''.b)
         tbuf = if @output_buffer.bytesize > 0
                  if number_of_bytes <= @output_buffer.bytesize
                    @output_buffer.slice!(0, number_of_bytes)
@@ -26,7 +26,7 @@ def read(number_of_bytes = nil, buf = '')
                    rbuf = sysread(number_of_bytes, buf)
                    out  = @output_buffer
                    out << rbuf if rbuf
-                   @output_buffer = ''
+                   @output_buffer = ''.b
                    out
                  end
                else
@@ -93,7 +93,7 @@ def ungetc(byte)
 
       def flush
         ret_val        = @output_buffer
-        @output_buffer = ''
+        @output_buffer = ''.b
         ret_val
       end
 
diff --git a/lib/zip/output_stream.rb b/lib/zip/output_stream.rb
index 3d1293ab..3dac2a48 100644
--- a/lib/zip/output_stream.rb
+++ b/lib/zip/output_stream.rb
@@ -62,7 +62,7 @@ def open(file_name, dep_encrypter = nil, encrypter: nil)
       end
 
       # Same as #open but writes to a filestream instead
-      def write_buffer(io = ::StringIO.new(''), dep_encrypter = nil, encrypter: nil)
+      def write_buffer(io = ::StringIO.new, dep_encrypter = nil, encrypter: nil)
         Zip.warn_about_v3_api('Zip::OutputStream.write_buffer') unless dep_encrypter.nil?
 
         io.binmode if io.respond_to?(:binmode)
diff --git a/lib/zip/pass_thru_decompressor.rb b/lib/zip/pass_thru_decompressor.rb
index e638540e..b51e19f1 100644
--- a/lib/zip/pass_thru_decompressor.rb
+++ b/lib/zip/pass_thru_decompressor.rb
@@ -5,7 +5,7 @@ def initialize(*args)
       @read_so_far = 0
     end
 
-    def read(length = nil, outbuf = '')
+    def read(length = nil, outbuf = ''.b)
       return (length.nil? || length.zero? ? '' : nil) if eof
 
       if length.nil? || (@read_so_far + length) > decompressed_size
diff --git a/test/encryption_test.rb b/test/encryption_test.rb
index d3ed5ffb..2feba1d9 100644
--- a/test/encryption_test.rb
+++ b/test/encryption_test.rb
@@ -19,7 +19,7 @@ def test_encrypt
     @rand = [250, 143, 107, 13, 143, 22, 155, 75, 228, 150, 12]
     @output = ::Zip::DOSTime.stub(:now, ::Zip::DOSTime.new(2014, 12, 17, 15, 56, 24)) do
       Random.stub(:rand, ->(_range) { @rand.shift }) do
-        Zip::OutputStream.write_buffer(::StringIO.new(''), Zip::TraditionalEncrypter.new('password')) do |zos|
+        Zip::OutputStream.write_buffer(::StringIO.new, Zip::TraditionalEncrypter.new('password')) do |zos|
           zos.put_next_entry('file1.txt')
           zos.write ::File.open(INPUT_FILE1).read
         end.string
diff --git a/test/file_test.rb b/test/file_test.rb
index ece14860..e596881e 100644
--- a/test/file_test.rb
+++ b/test/file_test.rb
@@ -503,7 +503,7 @@ def test_write_buffer
     zf = ::Zip::File.new(TEST_ZIP.zip_name)
     old_name = zf.entries.first
     zf.rename(old_name, new_name)
-    io = ::StringIO.new('')
+    io = ::StringIO.new
     buffer = zf.write_buffer(io)
     File.open(TEST_ZIP.zip_name, 'wb') { |f| f.write buffer.string }
     zf_read = ::Zip::File.new(TEST_ZIP.zip_name)
diff --git a/test/input_stream_test.rb b/test/input_stream_test.rb
index bfaf6dff..47ea7e05 100644
--- a/test/input_stream_test.rb
+++ b/test/input_stream_test.rb
@@ -136,7 +136,7 @@ def test_rewind
       assert_equal(TestZipFile::TEST_ZIP2.entry_names[0], e.name)
 
       # Do a little reading
-      buf = ''
+      buf = ''.b
       buf << zis.read(100)
       assert_equal(100, zis.pos)
       buf << (zis.gets || '')
@@ -145,7 +145,7 @@ def test_rewind
 
       zis.rewind
 
-      buf2 = ''
+      buf2 = ''.b
       buf2 << zis.read(100)
       buf2 << (zis.gets || '')
       buf2 << (zis.gets || '')
diff --git a/test/ioextras/abstract_output_stream_test.rb b/test/ioextras/abstract_output_stream_test.rb
index 9b02309c..cf5256ff 100644
--- a/test/ioextras/abstract_output_stream_test.rb
+++ b/test/ioextras/abstract_output_stream_test.rb
@@ -8,7 +8,7 @@ class TestOutputStream
     attr_accessor :buffer
 
     def initialize
-      @buffer = ''
+      @buffer = ''.b
     end
 
     def <<(data)
@@ -58,12 +58,12 @@ def test_print
     assert_equal("hello world. You ok out there?\nI sure hope so!\n", @output_stream.buffer)
 
     $, = 'X'
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.print('monkey', 'duck', 'zebra')
     assert_equal("monkeyXduckXzebra\n", @output_stream.buffer)
 
     $\ = nil
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.print(20)
     assert_equal('20', @output_stream.buffer)
   end
@@ -87,19 +87,19 @@ def test_puts
     @output_stream.puts('hello', 'world')
     assert_equal("\nhello\nworld\n", @output_stream.buffer)
 
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.puts("hello\n", "world\n")
     assert_equal("hello\nworld\n", @output_stream.buffer)
 
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.puts(%W[hello\n world\n])
     assert_equal("hello\nworld\n", @output_stream.buffer)
 
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.puts(%W[hello\n world\n], 'bingo')
     assert_equal("hello\nworld\nbingo\n", @output_stream.buffer)
 
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.puts(16, 20, 50, 'hello')
     assert_equal("16\n20\n50\nhello\n", @output_stream.buffer)
   end
diff --git a/test/output_stream_test.rb b/test/output_stream_test.rb
index b2f64ab9..02e59d64 100644
--- a/test/output_stream_test.rb
+++ b/test/output_stream_test.rb
@@ -23,7 +23,7 @@ def test_open
   end
 
   def test_write_buffer
-    io = ::StringIO.new('')
+    io = ::StringIO.new
     buffer = ::Zip::OutputStream.write_buffer(io) do |zos|
       zos.comment = TEST_ZIP.comment
       write_test_zip(zos)
@@ -33,7 +33,7 @@ def test_write_buffer
   end
 
   def test_write_buffer_binmode
-    io = ::StringIO.new('')
+    io = ::StringIO.new
     buffer = ::Zip::OutputStream.write_buffer(io) do |zos|
       zos.comment = TEST_ZIP.comment
       write_test_zip(zos)
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 76d57978..1b446bb5 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -145,7 +145,7 @@ class TestOutputStream
     attr_accessor :buffer
 
     def initialize
-      @buffer = ''
+      @buffer = ''.b
     end
 
     def <<(data)