diff --git a/ical.js b/ical.js
index 33b26d6..916fd3b 100644
--- a/ical.js
+++ b/ical.js
@@ -458,11 +458,10 @@ module.exports = {
           curr.end = (curr.datetype === 'date-time') ? new Date(curr.start.getTime()) : moment.utc(curr.start).add(1, 'days').toDate();
 
           // If there was a duration specified
+          // see RFC5545, 3.3.6 (no year and month)
           if (curr.duration !== undefined) {
             const durationUnits =
             {
-              // Y: 'years',
-              // M: 'months',
               W: 'weeks',
               D: 'days',
               H: 'hours',
@@ -470,15 +469,26 @@ module.exports = {
               S: 'seconds'
             };
             // Get the list of duration elements
-            const r = curr.duration.match(/-?\d{1,10}[YMWDHS]/g);
+            const duration = curr.duration.match(/-?\d{1,10}[WDHMS]/g);
 
             // Use the duration to create the end value, from the start
-            let newend = moment.utc(curr.start);
+            const startMoment = moment.utc(curr.start);
+            let newEnd = startMoment;
+
             // Is the 1st character a negative sign?
             const indicator = curr.duration.startsWith('-') ? -1 : 1;
-            newend = newend.add(Number.parseInt(r, 10) * indicator, durationUnits[r.toString().slice(-1)]);
+
+            for (const r of duration) {
+              const unit = r.slice(-1);
+              if (!durationUnits[unit]) {
+                throw new Error(`Invalid duration unit: ${unit}`);
+              }
+
+              newEnd = newEnd.add(Number.parseInt(r, 10) * indicator, durationUnits[r.toString().slice(-1)]);
+            }
+
             // End is a Date type, not moment
-            curr.end = newend.toDate();
+            curr.end = newEnd.toDate();
           }
         }
 
diff --git a/test/test-async.js b/test/test-async.js
index 220bd08..e86d218 100644
--- a/test/test-async.js
+++ b/test/test-async.js
@@ -851,7 +851,7 @@ vows
         },
         'it uses the start/end of the event'(event) {
           assert.equal(event.start.toJSON(), '2024-02-15T09:00:00.000Z');
-          assert.equal(event.end.toJSON(), '2024-02-15T09:15:00.000Z');
+          assert.equal(event.end.toJSON(), '2024-02-15T10:15:00.000Z');
         }
       }
     },
diff --git a/test/test.js b/test/test.js
index ddff525..2aefbfb 100644
--- a/test/test.js
+++ b/test/test.js
@@ -1041,7 +1041,7 @@ vows
         },
         'it uses the start/end of the event'(event) {
           assert.equal(event.start.toJSON(), '2024-02-15T09:00:00.000Z');
-          assert.equal(event.end.toJSON(), '2024-02-15T09:15:00.000Z');
+          assert.equal(event.end.toJSON(), '2024-02-15T10:15:00.000Z');
         }
       }
     },
diff --git a/test/test_date_time_duration.ics b/test/test_date_time_duration.ics
index f9ba846..b4308e8 100644
--- a/test/test_date_time_duration.ics
+++ b/test/test_date_time_duration.ics
@@ -13,6 +13,6 @@ DESCRIPTION:
 LOCATION:Kriftel
 X-APPLE-STRUCTURED-LOCATION;VALUE=URI;X-TITLE=Kriftel: geo:50.083558\,8.4693855
 DTSTART:20240215T090000Z
-DURATION:PT15M
+DURATION:PT1H15M
 END:VEVENT
 END:VCALENDAR