diff --git a/app/assets/stylesheets/components/messages.css b/app/assets/stylesheets/components/messages.css
index 479f543..926869a 100644
--- a/app/assets/stylesheets/components/messages.css
+++ b/app/assets/stylesheets/components/messages.css
@@ -229,6 +229,45 @@
   font-size: var(--font-size-sm);
 }
 
+summary.attachment-info {
+  cursor: pointer;
+}
+
+.attachment-summary-row {
+  display: flex;
+  gap: var(--spacing-3);
+  align-items: center;
+  width: 100%;
+}
+
+.attachment-download {
+  margin-left: auto;
+  font-size: var(--font-size-xs);
+  color: var(--color-text-link);
+  text-decoration: none;
+}
+
+.attachment-download:hover {
+  color: var(--color-text-link-hover);
+  text-decoration: underline;
+}
+
+.attachment-content {
+  margin-top: var(--spacing-2);
+  padding: var(--spacing-2);
+  background: var(--color-bg-container);
+  border: var(--border-width) solid var(--color-border);
+  border-radius: var(--border-radius-sm);
+  font-size: var(--font-size-xs);
+  overflow-x: auto;
+}
+
+.attachment-content code {
+  display: block;
+  font-family: var(--font-family-mono);
+  white-space: pre;
+}
+
 .filename {
   font-weight: var(--font-weight-medium);
   color: var(--color-text-primary);
diff --git a/app/controllers/attachments_controller.rb b/app/controllers/attachments_controller.rb
new file mode 100644
index 0000000..7ca7332
--- /dev/null
+++ b/app/controllers/attachments_controller.rb
@@ -0,0 +1,13 @@
+class AttachmentsController < ApplicationController
+  def show
+    attachment = Attachment.find(params[:id])
+    data = attachment.decoded_body
+    return head :not_found unless data
+
+    filename = attachment.file_name.presence || "attachment-#{attachment.id}"
+    content_type = attachment.content_type.presence || "application/octet-stream"
+
+    send_data data, filename: filename, type: content_type, disposition: "attachment"
+  end
+end
+
diff --git a/app/views/topics/_message.html.slim b/app/views/topics/_message.html.slim
index 7a8c7c3..b6298fa 100644
--- a/app/views/topics/_message.html.slim
+++ b/app/views/topics/_message.html.slim
@@ -41,10 +41,22 @@
       .message-attachments
         h4 Attachments:
         - message.attachments.each do |attachment|
-          .attachment
-            .attachment-info
-              span.filename = attachment.file_name
-              span.content-type = attachment.content_type if attachment.content_type
+          - if attachment.patch?
+            details.attachment
+              summary.attachment-info
+                span.attachment-summary-row
+                  span.filename = attachment.file_name
+                  span.content-type = attachment.content_type if attachment.content_type
+                  = link_to "Download", attachment_path(attachment), class: "attachment-download", download: attachment.file_name, data: { turbo: false }
+              pre.attachment-content
+                code.language-diff
+                  = attachment.decoded_body
+          - else
+            .attachment
+              .attachment-info
+                span.filename = attachment.file_name
+                span.content-type = attachment.content_type if attachment.content_type
+                = link_to "Download", attachment_path(attachment), class: "attachment-download", download: attachment.file_name, data: { turbo: false }
 
   - if message.import_log.present?
     .import-metadata
diff --git a/config/routes.rb b/config/routes.rb
index bb017a0..195122a 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -55,6 +55,7 @@
   get '/auth/:provider/callback', to: 'omniauth_callbacks#google_oauth2'
 
   post "messages/:id/read", to: "messages#read", as: :read_message
+  resources :attachments, only: [:show]
 
   if defined?(PgHero)
     constraints AdminConstraint.new do
diff --git a/spec/requests/topics_spec.rb b/spec/requests/topics_spec.rb
index 8d7ecdb..0f1175d 100644
--- a/spec/requests/topics_spec.rb
+++ b/spec/requests/topics_spec.rb
@@ -79,6 +79,17 @@
         reply_position = response.body.index(reply_message.body)
         expect(root_position).to be < reply_position
       end
+
+      it "renders patch attachments inline as expandable diff blocks" do
+        create(:attachment, :patch_file, message: root_message)
+
+        get topic_path(topic)
+
+        expect(response).to have_http_status(:success)
+        expect(response.body).to include("Attachments:")
+        expect(response.body).to include('class="language-diff"')
+        expect(response.body).to include("diff --git")
+      end
     end
 
     context "with nonexistent topic" do
@@ -89,6 +100,31 @@
     end
   end
 
+  describe "GET /attachments/:id" do
+    let!(:creator) { create(:alias) }
+    let!(:topic) { create(:topic, creator: creator) }
+    let!(:message) { create(:message, topic: topic, sender: creator, reply_to: nil, created_at: 2.hours.ago) }
+
+    it "streams the attachment as a download with the right filename" do
+      attachment = create(:attachment, :patch_file, message: message)
+
+      get attachment_path(attachment)
+
+      expect(response).to have_http_status(:success)
+      expect(response.headers["Content-Disposition"]).to include("attachment")
+      expect(response.headers["Content-Disposition"]).to include(attachment.file_name)
+      expect(response.body).to include("diff --git")
+    end
+
+    it "returns 404 when the attachment body is missing" do
+      attachment = create(:attachment, body: nil, message: message)
+
+      get attachment_path(attachment)
+
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
   describe "GET /topics/search" do
     let!(:creator1) { create(:alias) }
     let!(:creator2) { create(:alias) }