diff --git a/lib/__tests__/calendar-duplicate.test.ts b/lib/__tests__/calendar-duplicate.test.ts
index fae3b804d..d6b739f3b 100644
--- a/lib/__tests__/calendar-duplicate.test.ts
+++ b/lib/__tests__/calendar-duplicate.test.ts
@@ -28,6 +28,12 @@ describe('buildDuplicateEventData', () => {
     expect(data.virtualLocations).not.toBe(virtualLocations);
   });
 
+  // Without the type the copy's HTML would be stored, and shown, as text.
+  it('keeps the format of an HTML description', () => {
+    const data = buildDuplicateEventData(makeEvent({ description: '<p>Daily</p>', descriptionContentType: 'text/html' }));
+    expect(data).toMatchObject({ description: '<p>Daily</p>', descriptionContentType: 'text/html' });
+  });
+
   it('moves a timed event one day later in its own time zone with a fresh uid', () => {
     const data = buildDuplicateEventData(makeEvent());
     expect(data).toMatchObject({
diff --git a/lib/calendar-duplicate.ts b/lib/calendar-duplicate.ts
index 19895c9b5..437d08345 100644
--- a/lib/calendar-duplicate.ts
+++ b/lib/calendar-duplicate.ts
@@ -24,6 +24,8 @@ export function buildDuplicateEventData(event: CalendarEvent): Partial<CalendarE
     freeBusyStatus: event.freeBusyStatus,
     privacy: event.privacy,
   };
+  // Without its type an HTML description would be stored as plain text.
+  if (event.descriptionContentType) data.descriptionContentType = event.descriptionContentType;
   if (event.locations) data.locations = structuredClone(event.locations);
   if (event.virtualLocations) data.virtualLocations = structuredClone(event.virtualLocations);
   if (event.recurrenceRules) data.recurrenceRules = structuredClone(event.recurrenceRules);