diff --git a/lib/zip/file.rb b/lib/zip/file.rb
index 5ea27ea2..5c89606b 100644
--- a/lib/zip/file.rb
+++ b/lib/zip/file.rb
@@ -301,7 +301,7 @@ def commit
 
     # Write buffer write changes to buffer and return
     def write_buffer(io = ::StringIO.new)
-      return unless commit_required?
+      return io unless commit_required?
 
       ::Zip::OutputStream.write_buffer(io) do |zos|
         @cdir.each { |e| e.write_to_zip_output_stream(zos) }
diff --git a/test/file_test.rb b/test/file_test.rb
index b09f78bd..8179ce97 100644
--- a/test/file_test.rb
+++ b/test/file_test.rb
@@ -233,7 +233,7 @@ def test_open_buffer_without_block_write_buffer_does_nothing
     assert zf.entries.map(&:name).include?('zippedruby1.rb')
 
     # Ensure the buffer isn't changed.
-    zf.write_buffer(string_io)
+    assert_same(string_io, zf.write_buffer(string_io))
     assert_equal(data, string_io.string)
   end