diff --git a/CHANGELOG.adoc b/CHANGELOG.adoc
index 259588ffa77370c36ac98a4d0ef8b24b79a0dc8e..9ee7adf1f30f5c28a1be25652d9ebfbda22bbc48 100644
--- a/CHANGELOG.adoc
+++ b/CHANGELOG.adoc
@@ -23,6 +23,7 @@ For a detailed view of what's changed, refer to the {url-repo}/commits[commit hi
 * add default text to link that points to page outside of the aggregate document
 * scope IDs for pages not from current component (#37)
 * don't insert start page if it points outside current component version (#44)
+* convert reference to attachment in nav to external link if site URL is specified (#45)
 
 === Changed
 
diff --git a/packages/assembler/lib/produce-aggregate-document.js b/packages/assembler/lib/produce-aggregate-document.js
index 0baaba3bcf9ee84adc8469e7550dbb3007e236f6..002f95f410c6a2d0a15c3036daadb53dadd6d9b6 100644
--- a/packages/assembler/lib/produce-aggregate-document.js
+++ b/packages/assembler/lib/produce-aggregate-document.js
@@ -460,6 +460,7 @@ function aggregateAsciiDoc (
     } else {
       buffer.push('')
       // NOTE: try to toggle sectids; otherwise, fallback to globally unique synthetic ID
+      // Q: should we unset docname, page-module, etc?
       let toggleSectids, syntheticId
       if (!('sectids' in asciidocConfig.attributes)) {
         buffer.push(':!sectids:')
@@ -472,11 +473,16 @@ function aggregateAsciiDoc (
           syntheticId = `__object-id-${global.Opal.hash(outlineEntry).$object_id()}`
         }
       }
-      // Q: should we unset docname, page-module, etc?
-      const sectionTitle =
-        urlType === 'external'
-          ? `${url}[${navtitlePass ? navtitleAsciiDoc : navtitleAsciiDoc.replace(/\]/g, '\\]')}]`
-          : navtitleAsciiDoc
+      let sectionTitle = navtitleAsciiDoc
+      if (urlType === 'external') {
+        sectionTitle = `${url}[${navtitlePass ? navtitleAsciiDoc : navtitleAsciiDoc.replace(/\]/g, '\\]')}]`
+      } else if (urlType === 'internal' && !unresolved && siteUrl) {
+        const resource = contentCatalog.getFiles().find((it) => it.pub.url === url)
+        if (resource?.out) {
+          sectionTitle = navtitlePass ? navtitleAsciiDoc : navtitleAsciiDoc.replace(/\]/g, '\\]')
+          sectionTitle = `${siteUrl}${resource.pub.url}[${sectionTitle}]`
+        }
+      }
       let hlevel = level + 1
       if (hlevel > 6) {
         hlevel = 6
diff --git a/packages/assembler/test/produce-aggregate-documents-test.js b/packages/assembler/test/produce-aggregate-documents-test.js
index 3cf2341b71d65267f06d77ac6239f1c1f1741be4..8bcc52391e0d96de15c1d13b1251f93a23ed58cb 100644
--- a/packages/assembler/test/produce-aggregate-documents-test.js
+++ b/packages/assembler/test/produce-aggregate-documents-test.js
@@ -27,6 +27,10 @@ describe('produceAggregateDocuments()', () => {
     await runScenario('ignore-duplicate-nav-entry', __dirname)
   })
 
+  it('should handle navigation entry with attachment reference', async () => {
+    await runScenario('attachment-reference', __dirname)
+  })
+
   it('should handle navigation entry with external link', async () => {
     await runScenario('external-link', __dirname)
   })
diff --git a/packages/assembler/test/scenarios/attachment-reference/data.yml b/packages/assembler/test/scenarios/attachment-reference/data.yml
new file mode 100644
index 0000000000000000000000000000000000000000..35d34757bcc8d4b03ed5d9b8cc991a249a186ad1
--- /dev/null
+++ b/packages/assembler/test/scenarios/attachment-reference/data.yml
@@ -0,0 +1,19 @@
+name: the-component
+version: '1.0'
+title: The Component
+navigation:
+  items:
+  - content: xref:the-page.adoc[]
+  - content: xref:attachment$form.pdf[Form Title]
+files:
+- relative: the-page.adoc
+  contents: |-
+    = The Page Title
+
+    contents
+- relative: form.pdf
+  family: attachment
+assembler:
+  asciidoc:
+    attributes:
+      site-url: https://docs.example.org
diff --git a/packages/assembler/test/scenarios/attachment-reference/expects/the-component.adoc b/packages/assembler/test/scenarios/attachment-reference/expects/the-component.adoc
new file mode 100644
index 0000000000000000000000000000000000000000..ad3803939f6ac474da4b876e68a7863d0ddd370f
--- /dev/null
+++ b/packages/assembler/test/scenarios/attachment-reference/expects/the-component.adoc
@@ -0,0 +1,26 @@
+= The Component
+:revnumber: 1.0
+:doctype: book
+:underscore: _
+:page-component-name: the-component
+:page-component-version: 1.0
+:page-version: {page-component-version}
+:page-component-display-version: 1.0
+:page-component-title: The Component
+
+:docname: the-page
+:page-module: ROOT
+:page-relative-src-path: the-page.adoc
+:page-origin-url: https://github.com/acme/the-component
+:page-origin-start-path:
+:page-origin-refname: v1.0
+:page-origin-reftype: branch
+:page-origin-refhash: a00000000000000000000000000000000000000z
+[#the-page:::]
+== The Page Title
+
+contents
+
+:!sectids:
+== https://docs.example.org/the-component/1.0/_attachments/form.pdf[Form Title]
+:sectids: