diff --git a/client/src/components/Map/ReservationOverlay.tsx b/client/src/components/Map/ReservationOverlay.tsx
index b856482df..aff4154e6 100644
--- a/client/src/components/Map/ReservationOverlay.tsx
+++ b/client/src/components/Map/ReservationOverlay.tsx
@@ -83,6 +83,11 @@ function parseInTz(isoLocal: string, tz: string): number {
   const [y, mo, d] = datePart.split('-').map(Number)
   const [h, mi] = (timePart || '00:00').split(':').map(Number)
   const guess = Date.UTC(y, mo - 1, d, h, mi)
+  // A malformed date/time (e.g. an imported booking whose time is missing its
+  // minutes) makes Date.UTC NaN; bail before formatToParts, which throws on a
+  // non-finite date and would blank the whole trip. computeDuration's finiteness
+  // check then drops the duration cleanly.
+  if (!Number.isFinite(guess)) return NaN
   const fmt = new Intl.DateTimeFormat('en-US', {
     timeZone: tz, hour12: false,
     year: 'numeric', month: '2-digit', day: '2-digit',
diff --git a/client/src/components/Map/reservationsMapbox.test.ts b/client/src/components/Map/reservationsMapbox.test.ts
index 7a352649f..ab39319d6 100644
--- a/client/src/components/Map/reservationsMapbox.test.ts
+++ b/client/src/components/Map/reservationsMapbox.test.ts
@@ -93,6 +93,28 @@ describe('ReservationMapboxOverlay road routes (#1425)', () => {
   })
 })
 
+// A flight whose endpoints carry a malformed local_time (an imported booking
+// missing the minutes) plus timezones, so computeDuration takes the parseInTz
+// path. Pre-fix, Date.UTC → NaN and formatToParts threw mid-render (#1620).
+function malformedTimeFlight(): Reservation {
+  return {
+    id: 3, type: 'flight', status: 'confirmed',
+    reservation_time: '2024-01-15T22', reservation_end_time: '2024-01-16T08',
+    endpoints: [
+      { role: 'from', sequence: 0, name: 'JFK', code: 'JFK', lat: 40.6, lng: -73.8, timezone: 'America/New_York', local_date: '2024-01-15', local_time: '22' },
+      { role: 'to', sequence: 1, name: 'LHR', code: 'LHR', lat: 51.5, lng: -0.5, timezone: 'Europe/London', local_date: '2024-01-16', local_time: '08' },
+    ],
+  } as unknown as Reservation
+}
+
+describe('ReservationMapboxOverlay malformed times (#1620)', () => {
+  it('renders a flight with a malformed time instead of throwing on formatToParts', () => {
+    const map = fakeMap()
+    const overlay = new ReservationMapboxOverlay(map as never, opts, FakeMarker as never)
+    expect(() => overlay.update([malformedTimeFlight()], opts)).not.toThrow()
+  })
+})
+
 describe('ReservationMapboxOverlay transit routes (#1570)', () => {
   it('draws a transit journey with real geometry even when its stations project close together', () => {
     const map = fakeMap()
diff --git a/client/src/components/Map/reservationsMapbox.ts b/client/src/components/Map/reservationsMapbox.ts
index a698d21dd..bd5c849ee 100644
--- a/client/src/components/Map/reservationsMapbox.ts
+++ b/client/src/components/Map/reservationsMapbox.ts
@@ -51,6 +51,11 @@ function parseInTz(isoLocal: string, tz: string): number {
   const [y, mo, d] = datePart.split('-').map(Number)
   const [h, mi] = (timePart || '00:00').split(':').map(Number)
   const guess = Date.UTC(y, mo - 1, d, h, mi)
+  // A malformed date/time (e.g. an imported booking whose time is missing its
+  // minutes) makes Date.UTC NaN; bail before formatToParts, which throws on a
+  // non-finite date and would blank the whole trip. computeDuration's finiteness
+  // check then drops the duration cleanly.
+  if (!Number.isFinite(guess)) return NaN
   const fmt = new Intl.DateTimeFormat('en-US', {
     timeZone: tz, hour12: false,
     year: 'numeric', month: '2-digit', day: '2-digit',