diff --git a/lib/xz.rb b/lib/xz.rb
index afbef46..e3b7295 100644
--- a/lib/xz.rb
+++ b/lib/xz.rb
@@ -202,7 +202,7 @@ def decompress_stream(io, memory_limit: LibLZMA::UINT64_MAX, flags: [:tell_unsup
 
       LZMAError.raise_if_necessary(res)
 
-      res = ""
+      res = +""
       res.encode!(Encoding::BINARY)
       if block_given?
         res = lzma_code(io, stream) do |chunk|
@@ -310,7 +310,7 @@ def compress_stream(io, level: 6, check: :crc64, extreme: false, &block)
 
       LZMAError.raise_if_necessary(res)
 
-      res = ""
+      res = +""
       res.encode!(Encoding::BINARY)
       if block_given?
         res = lzma_code(io, stream, &block)
diff --git a/lib/xz/stream_reader.rb b/lib/xz/stream_reader.rb
index 37c3594..567bf8d 100644
--- a/lib/xz/stream_reader.rb
+++ b/lib/xz/stream_reader.rb
@@ -212,7 +212,7 @@ def read(length = nil, outbuf = String.new)
       # The user's request is in decompressed bytes, so it doesn't matter
       # how much is actually read from the compressed file.
       if @delegate_io.eof?
-        data   = ""
+        data   = +""
         action = XZ::LibLZMA::LZMA_FINISH
       else
         data   = @delegate_io.read(XZ::CHUNK_SIZE)
diff --git a/lib/xz/stream_writer.rb b/lib/xz/stream_writer.rb
index ba9a884..c382e6b 100644
--- a/lib/xz/stream_writer.rb
+++ b/lib/xz/stream_writer.rb
@@ -235,7 +235,7 @@ def write(*args)
   # Like superclass' method, but also ensures liblzma flushes all
   # compressed data to the delegate IO.
   def finish
-    lzma_code("", XZ::LibLZMA::LZMA_FINISH) { |compressed| @delegate_io.write(compressed) }
+    lzma_code(+"", XZ::LibLZMA::LZMA_FINISH) { |compressed| @delegate_io.write(compressed) }
     super
   end
 
diff --git a/ruby-xz.gemspec b/ruby-xz.gemspec
index 48991f4..d8e18be 100644
--- a/ruby-xz.gemspec
+++ b/ruby-xz.gemspec
@@ -60,6 +60,7 @@ GEMSPEC = Gem::Specification.new do |spec|
   spec.platform              = Gem::Platform::RUBY
   spec.post_install_message  = 'Version 1.0.0 of ruby-xz breaks the API. Read HISTORY.rdoc and adapt your code to the new API.'
 
+  spec.add_dependency 'fiddle', '~> 1.0.9'
   spec.add_development_dependency 'minitar', '~> 0.6'
   spec.add_development_dependency 'minitest', '~> 5.14'
   spec.add_development_dependency 'rake', '~> 13.0'