diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4b931da0..9b27cdb0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ### Unreleased
 
+- Fix `doc.file()` throwing when the same in-memory attachment is embedded twice under one name, because the creation and modified dates the deduplication check compares are absent for sources that are not read from disk
+
 ### [v0.20.1] - 2026-08-23
 
 - Add a Node ESM build so `import 'pdfkit'` in Node resolves to the Node build (real file system, native zlib, Node streams, self-registering standard fonts) instead of the browser bundle
diff --git a/lib/mixins/attachments.js b/lib/mixins/attachments.js
index 77114f30..e9f7e6eb 100644
--- a/lib/mixins/attachments.js
+++ b/lib/mixins/attachments.js
@@ -119,8 +119,20 @@ function isEqual(a, b) {
     a.Subtype === b.Subtype &&
     a.Params.CheckSum.toString() === b.Params.CheckSum.toString() &&
     a.Params.Size === b.Params.Size &&
-    a.Params.CreationDate.getTime() === b.Params.CreationDate.getTime() &&
-    ((a.Params.ModDate === undefined && b.Params.ModDate === undefined) ||
-      a.Params.ModDate.getTime() === b.Params.ModDate.getTime())
+    isSameDate(a.Params.CreationDate, b.Params.CreationDate) &&
+    isSameDate(a.Params.ModDate, b.Params.ModDate)
   );
 }
+
+/**
+ * Compare two dates, either of which may be absent.
+ *
+ * An in-memory source carries no file system timestamps, so `CreationDate` and
+ * `ModDate` are only present when the file was read from disk or the caller
+ * passed `creationDate` / `modifiedDate`. Two absent dates describe the same
+ * metadata; an absent date never matches a present one.
+ */
+function isSameDate(a, b) {
+  if (a === undefined || b === undefined) return a === b;
+  return a.getTime() === b.getTime();
+}
diff --git a/tests/unit/attachments.spec.js b/tests/unit/attachments.spec.js
index 6e49129b..d911526a 100644
--- a/tests/unit/attachments.spec.js
+++ b/tests/unit/attachments.spec.js
@@ -245,6 +245,90 @@ describe('file', () => {
     ]);
   });
 
+  test('attach the same file multiple times without dates', () => {
+    const docData = logData(document);
+
+    document.file(Buffer.from('example text'), { name: 'file1.txt' });
+    document.file(Buffer.from('example text'), { name: 'file1.txt' });
+    document.end();
+
+    const numFiles = docData.filter(
+      (str) =>
+        typeof str === 'string' && str.startsWith('<<\n/Type /EmbeddedFile\n'),
+    );
+
+    expect(numFiles.length).toEqual(1);
+
+    // both filespecs point at the single embedded file
+    expect(docData).toContainChunk([
+      `9 0 obj`,
+      `<<
+/Type /Filespec
+/AFRelationship /Unspecified
+/F (file1.txt)
+/EF <<
+/F 8 0 R
+>>
+/UF (file1.txt)
+>>`,
+    ]);
+
+    expect(docData).toContainChunk([
+      `10 0 obj`,
+      `<<
+/Type /Filespec
+/AFRelationship /Unspecified
+/F (file1.txt)
+/EF <<
+/F 8 0 R
+>>
+/UF (file1.txt)
+>>`,
+    ]);
+  });
+
+  test('attach the same file twice, only one with a creation date', () => {
+    const docData = logData(document);
+
+    document.file(Buffer.from('example text'), { name: 'file1.txt' });
+    document.file(Buffer.from('example text'), {
+      name: 'file1.txt',
+      creationDate: date,
+    });
+    document.end();
+
+    const numFiles = docData.filter(
+      (str) =>
+        typeof str === 'string' && str.startsWith('<<\n/Type /EmbeddedFile\n'),
+    );
+
+    // the metadata differs, so the reference is not reused
+    expect(numFiles.length).toEqual(2);
+  });
+
+  test('attach the same file twice, only one with a modified date', () => {
+    const docData = logData(document);
+
+    document.file(Buffer.from('example text'), {
+      name: 'file1.txt',
+      creationDate: date,
+    });
+    document.file(Buffer.from('example text'), {
+      name: 'file1.txt',
+      creationDate: date,
+      modifiedDate: date,
+    });
+    document.end();
+
+    const numFiles = docData.filter(
+      (str) =>
+        typeof str === 'string' && str.startsWith('<<\n/Type /EmbeddedFile\n'),
+    );
+
+    // the metadata differs, so the reference is not reused
+    expect(numFiles.length).toEqual(2);
+  });
+
   test('throws when the ref is missing', () => {
     expect(() =>
       document.addNamedEmbeddedFile('phantom.txt', undefined),