diff --git a/src/client.js b/src/client.js
index 9d4e96c83..351eba3e5 100644
--- a/src/client.js
+++ b/src/client.js
@@ -2112,7 +2112,20 @@ MatrixClient.prototype.getEventTimeline = function(timelineSet, eventId) {
     return promise;
 };
 
-MatrixClient.prototype._createMessagesRequest = function(roomId, fromToken, limit, dir, timelineFilter = undefined) {
+/**
+ * Makes a request to /messages with the appropriate lazy loading filter set.
+ * XXX: if we do get rid of scrollback (as it's not used at the moment),
+ * we could inline this method again in paginateEventTimeline as that would
+ * then be the only call-site
+ * @param {string} roomId
+ * @param {string} fromToken
+ * @param {number} limit the maximum amount of events the retrieve
+ * @param {string} dir 'f' or 'b'
+ * @param {Filter} timelineFilter the timeline filter to pass
+ * @return {Promise}
+ */
+MatrixClient.prototype._createMessagesRequest =
+function(roomId, fromToken, limit, dir, timelineFilter = undefined) {
     const path = utils.encodeUri(
         "/rooms/$roomId/messages", {$roomId: roomId},
     );
@@ -2139,8 +2152,7 @@ MatrixClient.prototype._createMessagesRequest = function(roomId, fromToken, limi
         params.filter = JSON.stringify(filter);
     }
     return this._http.authedRequest(undefined, "GET", path, params);
-}
-
+};
 
 /**
  * Take an EventTimeline, and back/forward-fill results.
diff --git a/src/models/room-state.js b/src/models/room-state.js
index 48f2b68ba..cbabacc1c 100644
--- a/src/models/room-state.js
+++ b/src/models/room-state.js
@@ -262,15 +262,23 @@ RoomState.prototype.clone = function() {
     return copy;
 };
 
-
+/**
+ * Add previously unknown state events just before
+ * prepending events to the timeline.
+ * When lazy loading members while back-paginating,
+ * the relevant room state for the timeline chunk at the end
+ * of the chunk can be set with this method.
+ * @param {MatrixEvent[]} events state events to prepend
+ */
 RoomState.prototype.prependStateEvents = function(events) {
     const unknownStateEvents = events.filter((event) => {
         return this.events[event.getType()] === undefined ||
             this.events[event.getType()][event.getStateKey()] === undefined;
     });
 
-    return this.setStateEvents(unknownStateEvents);
-}
+    this.setStateEvents(unknownStateEvents);
+};
+
 /**
  * Add an array of one or more state MatrixEvents, overwriting
  * any existing state with the same {type, stateKey} tuple. Will fire