diff --git a/app/endpoints/ical.js b/app/endpoints/ical.js
index 82c18353..8d2e9299 100644
--- a/app/endpoints/ical.js
+++ b/app/endpoints/ical.js
@@ -24,12 +24,19 @@ const { EventsRange } = require("../models/calConst");
 const dt = require("../util/dateTime");
 const config = require("../config");
 
+// shown in the description when the organizer didn't give a duration
+// and the feed had to assume one. re: #498
+const UNSPECIFIED_DURATION =
+  "The organizer didn't specify an end time, so this entry assumes 1 hour.";
+
 module.exports = {
 // endpoint export:
   get,
 // export for testing:
   escapeBreak,
   replace,
+  buildCalEntry,
+  UNSPECIFIED_DURATION,
 };
 
 // text|escapeBreak("HEADER") => HEADER:text
@@ -249,6 +256,15 @@ function buildCalEntry(evt, at) {
     description: [
       news,
       evt.descr, evt.timedetails,
+      // a v-event needs an end time, so addDuration() invents one hour when the
+      // organizer didn't give a duration. say so: otherwise the entry looks just
+      // as definite as one with a real end time. re: #498
+      //
+      // only when there's no timedetails though: that's free text like
+      // "meet 7pm, roll 7:30" and it prints on the line above. saying the
+      // organizer gave no end time directly under their own note about the
+      // timing reads as a contradiction.
+      (!evt.hasDuration() && !evt.timedetails) ? UNSPECIFIED_DURATION : null,
       evt.locend? "Ends at "+ evt.locend: null,
       url
     ],
diff --git a/app/models/calEvent.js b/app/models/calEvent.js
index d004edfc..f58d9176 100644
--- a/app/models/calEvent.js
+++ b/app/models/calEvent.js
@@ -108,7 +108,13 @@ const methods =  {
   // generates a 1 hour duration if none was specified.
   addDuration(start) {
     const len = this.eventduration;
-    return endTime = (len > 0) ? start.add(len, 'minute') : start.add(1, 'hour');
+    return (len > 0) ? start.add(len, 'minute') : start.add(1, 'hour');
+  },
+
+  // true when the organizer gave an explicit duration;
+  // false when addDuration() would have to invent one.
+  hasDuration() {
+    return this.eventduration > 0;
   },
 
   // remove this record and any associated caldaily(s) from the database.
diff --git a/app/test/ical_test.js b/app/test/ical_test.js
index 9fc1c723..e58809fe 100644
--- a/app/test/ical_test.js
+++ b/app/test/ical_test.js
@@ -6,6 +6,8 @@ const testdb = require("./testdb");
 const { CalEvent } = require("../models/calEvent");
 const { CalDaily } = require("../models/calDaily");
 const { EventStatus } = require("../models/calConst");
+const ical = require("../endpoints/ical");
+const dt = require("../util/dateTime");
 //
 const { describe, it, before, after } = require("node:test");
 const assert = require("node:assert/strict");
@@ -281,3 +283,53 @@ String.raw`BEGIN:VCALENDAR`,
 String.raw`END:VCALENDAR`,
 "" // trailing new line. i think.
 ].join("\r\n");
+
+// buildCalEntry is a pure function, so these need no database.
+// re: #498 -- and the "nil and zero" todo in "can handle a canceled event".
+describe("ical duration", () => {
+  const day = dt.fromYMDString("2002-08-01");
+
+  // build the pieces buildCalEntry() needs for one occurrence.
+  function entryFor(eventduration, timedetails = null) {
+    const evt = CalEvent.wrap({
+      id: 1, title: "Test Ride", name: "organizer",
+      descr: "details", eventtime: "19:00:00", eventduration, timedetails,
+      created: day.toDate(), modified: day.toDate(), changes: 0,
+    });
+    const at = CalDaily.wrap({
+      pkid: 201, id: 1, eventdate: day.toDate(),
+      eventstatus: EventStatus.Active, newsflash: null,
+    });
+    return ical.buildCalEntry(evt, at);
+  }
+
+  it("notes the assumed duration when the organizer gave none", () => {
+    for (const none of [null, 0, undefined]) {
+      const entry = entryFor(none);
+      assert.ok(entry.description.includes(ical.UNSPECIFIED_DURATION),
+        `expected the note for eventduration ${JSON.stringify(none)}`);
+      // the invented end time is one hour after the start
+      assert.equal(entry.end.diff(entry.start, 'minute'), 60);
+    }
+  });
+
+  it("says nothing when the organizer gave a duration", () => {
+    const entry = entryFor(90);
+    assert.ok(!entry.description.includes(ical.UNSPECIFIED_DURATION),
+      "did not expect the note when a duration was supplied");
+    assert.equal(entry.end.diff(entry.start, 'minute'), 90);
+  });
+
+  // a ride without a duration may still describe its timing in free text,
+  // which prints just above this note; repeating it there reads as a
+  // contradiction. re: #498
+  it("says nothing when timedetails already covers the timing", () => {
+    const entry = entryFor(null, "meet 7pm, roll 7:30");
+    assert.ok(!entry.description.includes(ical.UNSPECIFIED_DURATION),
+      "did not expect the note alongside timedetails");
+    assert.ok(entry.description.includes("meet 7pm, roll 7:30"),
+      "expected the organizer's own timing note to still be there");
+    // the end time is still assumed; we just don't say so twice.
+    assert.equal(entry.end.diff(entry.start, 'minute'), 60);
+  });
+});