diff --git a/CHANGELOG.md b/CHANGELOG.md
index 66d0416ae..134afbde6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,11 @@ Please visit [cucumber/CONTRIBUTING.md](https://github.com/cucumber/cucumber/blo
 ### Changed
 - Heavy refactor to the internals for message building (Used in formatters - should be no noticeable change)
   ([#1853](https://github.com/cucumber/cucumber-ruby/pull/1853) [luke-hill](https://github.com/luke-hill))
+- Simplify attachment handling in the `MessageBuilder` and `#attach` method
+
+([#1853](
+### Fixed
+- When someone `#attach`s a hashified output (Instead of JSON), call `#to_json` before attaching as a stringified JSON response
 
 ## [11.0.0] - 2026-04-14
 ### Added
diff --git a/features/docs/fixtures/cucumber.jpeg b/features/docs/fixtures/cucumber.jpeg
new file mode 100644
index 000000000..e833d6c77
Binary files /dev/null and b/features/docs/fixtures/cucumber.jpeg differ
diff --git a/features/docs/writing_support_code/attachments.feature b/features/docs/writing_support_code/attachments.feature
index d868abc19..afe39eae8 100644
--- a/features/docs/writing_support_code/attachments.feature
+++ b/features/docs/writing_support_code/attachments.feature
@@ -20,18 +20,15 @@ Feature: Attachments
         Scenario:
           Given I attach a screenshot without a media type
       """
-    And a file named "features/screenshot.png" with:
-      """
-      foo
-      """
+    And an image named "cucumber.jpeg"
     And a file named "features/step_definitions/attaching_screenshot_steps.rb" with:
       """
       Given('I attach a screenshot with a media type') do
-        attach('features/screenshot.png', 'image/png')
+        attach('features/cucumber.jpeg', 'image/jpeg')
       end
 
       Given('I attach a screenshot without a media type') do
-        attach('features/screenshot.png')
+        attach('features/cucumber.jpeg')
       end
       """
 
@@ -39,18 +36,18 @@ Feature: Attachments
     When I run `cucumber --format message features/attaching_screenshot_with_mediatype.feature`
     Then output should be valid NDJSON
     And the output should contain NDJSON with key "attachment"
-    And the output should contain NDJSON "attachment" message with key "body" and value "Zm9v"
-    And the output should contain NDJSON "attachment" message with key "mediaType" and value "image/png"
+    And the output should contain NDJSON "attachment" message with key "body" and an encoded value
+    And the output should contain NDJSON "attachment" message with key "mediaType" and value "image/jpeg"
     
   Scenario: Media type is inferred from the given file
     When I run `cucumber --format message features/attaching_screenshot_without_mediatype.feature`
     Then output should be valid NDJSON
     And the output should contain NDJSON with key "attachment"
-    And the output should contain NDJSON "attachment" message with key "body" and value "Zm9v"
-    And the output should contain NDJSON "attachment" message with key "mediaType" and value "image/png"
+    And the output should contain NDJSON "attachment" message with key "body" and an encoded value
+    And the output should contain NDJSON "attachment" message with key "mediaType" and value "image/jpeg"
 
   Scenario: With json formatter, files can be attached given their path
     When I run `cucumber --format json features/attaching_screenshot_with_mediatype.feature`
     Then the output should contain "embeddings\":"
-    And the output should contain "\"mime_type\": \"image/png\","
-    And the output should contain "\"data\": \"Zm9v\""
+    And the output should contain "\"mime_type\": \"image/jpeg\","
+    And the output should contain "\"data\":"
diff --git a/features/lib/step_definitions/cucumber_steps.rb b/features/lib/step_definitions/cucumber_steps.rb
index dc7c830d3..9b33e62a3 100644
--- a/features/lib/step_definitions/cucumber_steps.rb
+++ b/features/lib/step_definitions/cucumber_steps.rb
@@ -15,7 +15,7 @@
     '    @io = config.out_stream',
     '  end',
     '',
-    '  def attach(src, media_type, _filename)',
+    '  def attach(src, media_type, _filename, _streamed_file)',
     '    @io.puts(src)',
     '  end',
     'end'
diff --git a/features/lib/step_definitions/filesystem_steps.rb b/features/lib/step_definitions/filesystem_steps.rb
index ce719214d..a85cb8b82 100644
--- a/features/lib/step_definitions/filesystem_steps.rb
+++ b/features/lib/step_definitions/filesystem_steps.rb
@@ -8,6 +8,10 @@
   write_file(path, content)
 end
 
+Given('an image named {string}') do |name|
+  copy_image_named(name)
+end
+
 Given('an empty file named {string}') do |path|
   write_file(path, '')
 end
diff --git a/features/lib/step_definitions/message_steps.rb b/features/lib/step_definitions/message_steps.rb
index 4996bf88b..40dec1927 100644
--- a/features/lib/step_definitions/message_steps.rb
+++ b/features/lib/step_definitions/message_steps.rb
@@ -18,6 +18,12 @@
   expect(command_line.stdout).to match(/"#{key}": ?"#{value}"/)
 end
 
+Then('the output should contain NDJSON {string} message with key {string} and an encoded value') do |message_name, key|
+  message_contents = command_line.stdout(format: :messages).detect { |msg| msg.keys == [message_name] }[message_name]
+
+  expect(message_contents[key].length).to be > 50
+end
+
 Then('the output should contain NDJSON {string} message with key {string} and value {string}') do |message_name, key, value|
   message_contents = command_line.stdout(format: :messages).detect { |msg| msg.keys == [message_name] }[message_name]
 
diff --git a/features/lib/support/filesystem.rb b/features/lib/support/filesystem.rb
index fa99b5a83..d12d13d80 100644
--- a/features/lib/support/filesystem.rb
+++ b/features/lib/support/filesystem.rb
@@ -4,3 +4,8 @@ def write_file(path, content)
   FileUtils.mkdir_p(File.dirname(path))
   File.open(path, 'w') { |file| file.write(content) }
 end
+
+def copy_image_named(name)
+  fixture_dir = File.expand_path('../../features/docs/fixtures')
+  FileUtils.cp("#{fixture_dir}/#{name}", "#{Dir.pwd}/features/#{name}")
+end
diff --git a/lib/cucumber/formatter/console.rb b/lib/cucumber/formatter/console.rb
index dfe7688ae..194698f56 100644
--- a/lib/cucumber/formatter/console.rb
+++ b/lib/cucumber/formatter/console.rb
@@ -169,7 +169,7 @@ def do_print_passing_wip(passed_messages)
         end
       end
 
-      def attach(src, media_type, filename)
+      def attach(src, media_type, filename, _streamed_file)
         return unless media_type == 'text/x.cucumber.log+plain'
         return unless @io
 
diff --git a/lib/cucumber/formatter/json.rb b/lib/cucumber/formatter/json.rb
index 8fc8471a4..401d762cb 100644
--- a/lib/cucumber/formatter/json.rb
+++ b/lib/cucumber/formatter/json.rb
@@ -85,7 +85,7 @@ def on_test_run_finished(_event)
         @io.write(JSON.pretty_generate(@feature_hashes))
       end
 
-      def attach(src, mime_type, _filename)
+      def attach(src, mime_type, _filename, _streamed_file)
         if mime_type == 'text/x.cucumber.log+plain'
           test_step_output << src
           return
diff --git a/lib/cucumber/formatter/message_builder.rb b/lib/cucumber/formatter/message_builder.rb
index 86a0e9204..92f5335a8 100644
--- a/lib/cucumber/formatter/message_builder.rb
+++ b/lib/cucumber/formatter/message_builder.rb
@@ -1,8 +1,9 @@
 # frozen_string_literal: true
 
 require 'base64'
-require 'cucumber/formatter/backtrace_filter'
+require 'json'
 
+require 'cucumber/formatter/backtrace_filter'
 require 'cucumber/query'
 
 module Cucumber
@@ -55,7 +56,7 @@ def initialize(config)
         config.on_event :undefined_parameter_type, &method(:on_undefined_parameter_type)
       end
 
-      def attach(src, media_type, filename)
+      def attach(src, media_type, filename, streamed_file)
         attachment_data = {
           test_step_id: @current_test_step_id,
           test_case_started_id: @current_test_case_started_id,
@@ -64,13 +65,12 @@ def attach(src, media_type, filename)
           timestamp: time_to_timestamp(Time.now)
         }
 
-        if media_type&.start_with?('text/')
-          attachment_data[:content_encoding] = Cucumber::Messages::AttachmentContentEncoding::IDENTITY
-          attachment_data[:body] = src
-        else
-          body = src.respond_to?(:read) ? src.read : src
+        if streamed_file
           attachment_data[:content_encoding] = Cucumber::Messages::AttachmentContentEncoding::BASE64
-          attachment_data[:body] = Base64.strict_encode64(body)
+          attachment_data[:body] = Base64.strict_encode64(src)
+        else
+          attachment_data[:content_encoding] = Cucumber::Messages::AttachmentContentEncoding::IDENTITY
+          attachment_data[:body] = src.is_a?(Hash) ? src.to_json : src
         end
 
         message = Cucumber::Messages::Envelope.new(attachment: Cucumber::Messages::Attachment.new(**attachment_data))
diff --git a/lib/cucumber/formatter/pretty.rb b/lib/cucumber/formatter/pretty.rb
index 97ba8d796..7f4549703 100644
--- a/lib/cucumber/formatter/pretty.rb
+++ b/lib/cucumber/formatter/pretty.rb
@@ -140,7 +140,7 @@ def on_test_run_finished(_event)
         print_summary
       end
 
-      def attach(src, media_type, filename)
+      def attach(src, media_type, filename, _streamed_file)
         return unless media_type == 'text/x.cucumber.log+plain'
 
         if filename
diff --git a/lib/cucumber/glue/proto_world.rb b/lib/cucumber/glue/proto_world.rb
index 83452aa8d..a797d34b8 100644
--- a/lib/cucumber/glue/proto_world.rb
+++ b/lib/cucumber/glue/proto_world.rb
@@ -93,10 +93,12 @@ def attach(file, media_type = nil, filename = nil)
         if File.file?(file)
           media_type = MiniMime.lookup_by_filename(file)&.content_type if media_type.nil?
           file = File.read(file, mode: 'rb')
+          streamed_file = true
         end
-        super
+        # We pass in the concept of whether the file is streamed to ensure that the envelope encoding is correct
+        super(file, media_type, filename, streamed_file)
       rescue StandardError
-        super
+        super(file, media_type, filename, streamed_file)
       end
 
       # Mark the matched step as pending.
@@ -153,8 +155,8 @@ def add_modules!(world_modules, namespaced_world_modules)
             runtime.ask(question, timeout_seconds)
           end
 
-          define_method(:attach) do |file, media_type, filename|
-            runtime.attach(file, media_type, filename)
+          define_method(:attach) do |file, media_type, filename, streamed_file|
+            runtime.attach(file, media_type, filename, streamed_file)
           end
 
           # Prints the list of modules that are included in the World
diff --git a/lib/cucumber/runtime/user_interface.rb b/lib/cucumber/runtime/user_interface.rb
index 433ef8273..1621d87f8 100644
--- a/lib/cucumber/runtime/user_interface.rb
+++ b/lib/cucumber/runtime/user_interface.rb
@@ -41,8 +41,8 @@ def ask(question, timeout_seconds)
       # be a path to a file, or if it's an image it may also be a Base64 encoded image.
       # The embedded data may or may not be ignored, depending on what kind of formatter(s) are active.
       #
-      def attach(src, media_type, filename)
-        @visitor.attach(src, media_type, filename)
+      def attach(src, media_type, filename, streamed_file)
+        @visitor.attach(src, media_type, filename, streamed_file)
       end
 
       private
diff --git a/spec/cucumber/glue/step_definition_spec.rb b/spec/cucumber/glue/step_definition_spec.rb
index c377d7816..89514268c 100644
--- a/spec/cucumber/glue/step_definition_spec.rb
+++ b/spec/cucumber/glue/step_definition_spec.rb
@@ -63,7 +63,7 @@ def step_match(text)
         it 'calls a method on the world when specified with a symbol' do
           expect(registry.current_world).to receive(:with_symbol)
 
-          dsl.Given(/With symbol/, :with_symbol)
+          dsl.Given('With symbol', :with_symbol)
 
           run_step 'With symbol'
         end
@@ -71,7 +71,7 @@ def step_match(text)
         it 'calls a method on a specified object' do
           allow(registry.current_world).to receive(:target) { target }
 
-          dsl.Given(/With symbol on block/, :with_symbol, on: -> { target })
+          dsl.Given('With symbol on block', :with_symbol, on: -> { target })
 
           expect(target).to receive(:with_symbol)
 
@@ -81,7 +81,7 @@ def step_match(text)
         it 'calls a method on a specified world attribute' do
           allow(registry.current_world).to receive(:target) { target }
 
-          dsl.Given(/With symbol on symbol/, :with_symbol, on: :target)
+          dsl.Given('With symbol on symbol', :with_symbol, on: :target)
 
           expect(target).to receive(:with_symbol)
 
@@ -102,17 +102,15 @@ def step_match(text)
       end
 
       it 'raises UndefinedDynamicStep when an undefined step is parsed dynamically' do
-        dsl.Given(/Outside/) do
-          steps %(
-            Given Inside
-          )
+        dsl.Given('Outside') do
+          steps %(Given Inside)
         end
 
         expect { run_step 'Outside' }.to raise_error(Cucumber::UndefinedDynamicStep)
       end
 
       it 'raises UndefinedDynamicStep when an undefined step with doc string is parsed dynamically' do
-        dsl.Given(/Outside/) do
+        dsl.Given('Outside') do
           steps %(
             Given Inside
             """
@@ -125,7 +123,7 @@ def step_match(text)
       end
 
       it 'raises UndefinedDynamicStep when an undefined step with data table is parsed dynamically' do
-        dsl.Given(/Outside/) do
+        dsl.Given('Outside') do
           steps %(
             Given Inside
              | a |
@@ -193,14 +191,14 @@ def step_match(text)
 
       describe '#log' do
         it 'calls "attach" with the correct media type' do
-          expect(user_interface).to receive(:attach).with('wasup', 'text/x.cucumber.log+plain', nil)
+          expect(user_interface).to receive(:attach).with('wasup', 'text/x.cucumber.log+plain', nil, nil)
 
           dsl.Given('Loud') { log 'wasup' }
           run_step 'Loud'
         end
 
         it 'calls `to_s` if the message is not a String' do
-          expect(user_interface).to receive(:attach).with('["Not", 1, "string"]', 'text/x.cucumber.log+plain', nil)
+          expect(user_interface).to receive(:attach).with('["Not", 1, "string"]', 'text/x.cucumber.log+plain', nil, nil)
 
           dsl.Given('Loud') { log ['Not', 1, 'string'] }
           run_step 'Loud'