diff --git a/src/web/auto-reply.web-auto-reply.reconnects-after-connection-close.test.ts b/src/web/auto-reply.web-auto-reply.reconnects-after-connection-close.test.ts
index 9c6bcd37ef6..c096253729e 100644
--- a/src/web/auto-reply.web-auto-reply.reconnects-after-connection-close.test.ts
+++ b/src/web/auto-reply.web-auto-reply.reconnects-after-connection-close.test.ts
@@ -106,6 +106,11 @@ describe("web auto-reply", () => {
     vi.useRealTimers();
   });
 
+  it("handles helper envelope timestamps with trimmed timezones (regression)", () => {
+    const d = new Date("2025-01-01T00:00:00.000Z");
+    expect(() => formatEnvelopeTimestamp(d, " America/Los_Angeles ")).not.toThrow();
+  });
+
   it("reconnects after a connection close", async () => {
     const closeResolvers: Array<() => void> = [];
     const sleep = vi.fn(async () => {});
diff --git a/test/helpers/envelope-timestamp.ts b/test/helpers/envelope-timestamp.ts
index f86c90d7660..70c6bbe58c2 100644
--- a/test/helpers/envelope-timestamp.ts
+++ b/test/helpers/envelope-timestamp.ts
@@ -8,7 +8,8 @@ export { escapeRegExp } from "../../src/utils.js";
 type EnvelopeTimestampZone = string;
 
 export function formatEnvelopeTimestamp(date: Date, zone: EnvelopeTimestampZone = "utc"): string {
-  const normalized = zone.trim().toLowerCase();
+  const trimmedZone = zone.trim();
+  const normalized = trimmedZone.toLowerCase();
   const weekday = (() => {
     try {
       if (normalized === "utc" || normalized === "gmt") {
@@ -17,7 +18,9 @@ export function formatEnvelopeTimestamp(date: Date, zone: EnvelopeTimestampZone
       if (normalized === "local" || normalized === "host") {
         return new Intl.DateTimeFormat("en-US", { weekday: "short" }).format(date);
       }
-      return new Intl.DateTimeFormat("en-US", { timeZone: zone, weekday: "short" }).format(date);
+      return new Intl.DateTimeFormat("en-US", { timeZone: trimmedZone, weekday: "short" }).format(
+        date,
+      );
     } catch {
       return undefined;
     }
@@ -31,7 +34,7 @@ export function formatEnvelopeTimestamp(date: Date, zone: EnvelopeTimestampZone
     const ts = formatZonedTimestamp(date) ?? formatUtcTimestamp(date);
     return weekday ? `${weekday} ${ts}` : ts;
   }
-  const ts = formatZonedTimestamp(date, { timeZone: zone }) ?? formatUtcTimestamp(date);
+  const ts = formatZonedTimestamp(date, { timeZone: trimmedZone }) ?? formatUtcTimestamp(date);
   return weekday ? `${weekday} ${ts}` : ts;
 }