diff --git a/lib/models/room.js b/lib/models/room.js
index d56c353c8..c56374547 100644
--- a/lib/models/room.js
+++ b/lib/models/room.js
@@ -595,18 +595,22 @@ Room.prototype._addLiveEvents = function(events) {
             // remote echo of an event we sent earlier
             var existingEvent = this._txnToEvent[events[i].getUnsigned().transaction_id];
             if (existingEvent) {
+                var oldEventId = existingEvent.getId();
+
                 // no longer pending
                 delete this._txnToEvent[events[i].getUnsigned().transaction_id];
 
                 // update the timeline map, because the event id has changed
-                var existingTimeline = this._eventIdToTimeline[existingEvent.getId()];
+                var existingTimeline = this._eventIdToTimeline[oldEventId];
                 if (existingTimeline) {
-                    delete this._eventIdToTimeline[existingEvent.getId()];
+                    delete this._eventIdToTimeline[oldEventId];
                     this._eventIdToTimeline[events[i].getId()] = existingTimeline;
                 }
 
                 // replace the event source
                 existingEvent.event = events[i].event;
+
+                this.emit("Room.localEchoUpdated", existingEvent, this, oldEventId);
                 continue;
             }
         }
@@ -1315,3 +1319,21 @@ module.exports = Room;
  *   }
  * });
  */
+
+/**
+ * Fires when a local-echo of a transmitted event is replaced by its remote-echo.
+ *
+ * <p>When an event is first transmitted, then (assuming the /send completes
+ * before the event comes back from /sync), a temporary copy of the event is
+ * inserted into the timeline, with a temporary event id. Once the echo comes
+ * back from the server, the event is replaced by the complete event from the
+ * homeserver, thus updating its event id.
+ *
+ * <p>If the event comes back from /sync before the /send completes, the
+ * temporary event id is never stored, and this event is not raised.
+ *
+ * @event module:client~MatrixClient#"Room.localEchoUpdated"
+ * @param {MatrixEvent} event The matrix event which has been updated
+ * @param {Room} room The room containing the redacted event
+ * @param {string} oldEventId The temporary event id which has been replaced
+ */
diff --git a/lib/sync.js b/lib/sync.js
index a0e1442c1..73b695643 100644
--- a/lib/sync.js
+++ b/lib/sync.js
@@ -86,7 +86,9 @@ SyncApi.prototype.createRoom = function(roomId) {
     });
     reEmit(client, room, ["Room.name", "Room.timeline", "Room.redaction",
                           "Room.receipt", "Room.tags",
-                          "Room.timelineReset"]);
+                          "Room.timelineReset",
+                          "Room.localEchoUpdated",
+                         ]);
     this._registerStateListeners(room);
     return room;
 };
diff --git a/spec/unit/room.spec.js b/spec/unit/room.spec.js
index da6ae7e1d..1e3a6919b 100644
--- a/spec/unit/room.spec.js
+++ b/spec/unit/room.spec.js
@@ -328,6 +328,39 @@ describe("Room", function() {
             room.addEventsToTimeline(events);
             expect(room.getEventReadUpTo(userA)).toEqual(events[1].getId());
         });
+
+        it("should emit Room.localEchoUpdated when a local echo is updated", function() {
+            var localEvent = utils.mkMessage({
+                room: roomId, user: userA, event: true,
+            });
+            localEvent._txnId = "TXN_ID";
+            localEvent.status = EventStatus.SENDING;
+            var localEventId = localEvent.getId();
+
+            var remoteEvent = utils.mkMessage({
+                room: roomId, user: userA, event: true,
+            });
+            remoteEvent.event.unsigned = {transaction_id: "TXN_ID"};
+            var remoteEventId = remoteEvent.getId();
+
+            var callCount = 0;
+            room.on("Room.localEchoUpdated", function(event, emitRoom, oldEventId) {
+                callCount += 1;
+                expect(event.getId()).toEqual(remoteEventId);
+                expect(emitRoom).toEqual(room);
+                expect(oldEventId).toEqual(localEventId);
+            });
+
+            // first add the local echo to the timeline
+            room.addEventsToTimeline([localEvent]);
+            expect(room.timeline.length).toEqual(1);
+
+            // then the remoteEvent
+            room.addEventsToTimeline([remoteEvent]);
+            expect(room.timeline.length).toEqual(1);
+
+            expect(callCount).toEqual(1);
+        });
     });
 
     var resetTimelineTests = function(timelineSupport) {