diff --git a/src/models/event.js b/src/models/event.js
index 76544b6da..ba5abf366 100644
--- a/src/models/event.js
+++ b/src/models/event.js
@@ -730,6 +730,16 @@ utils.extend(module.exports.MatrixEvent.prototype, {
         // successfully sent.
         this.status = null;
     },
+
+    /**
+     * Get whether the event is a relation event.
+     * @return {boolean}
+     */
+    isRelation() {
+        const content = this.getContent();
+        const relation = content && content["m.relates_to"];
+        return relation && relation.rel_type && relation.event_id;
+    },
 });
 
 
diff --git a/src/models/room.js b/src/models/room.js
index e50edf07b..b0930f38b 100644
--- a/src/models/room.js
+++ b/src/models/room.js
@@ -1101,7 +1101,11 @@ Room.prototype.addPendingEvent = function(event, txnId) {
 
     this._txnToEvent[txnId] = event;
 
-    if (this._opts.pendingEventOrdering == "detached") {
+    // TODO: We currently ignore `pendingEventOrdering` for relation events.
+    // They are aggregated by the timeline set, and we want that to happen right
+    // away for easy local echo, but it complicates what should be a general
+    // code path by branching on the event type.
+    if (!event.isRelation() && this._opts.pendingEventOrdering == "detached") {
         if (this._pendingEventList.some((e) => e.status === EventStatus.NOT_SENT)) {
             console.warn("Setting event as NOT_SENT due to messages in the same state");
             event.status = EventStatus.NOT_SENT;