diff --git a/lib/models/event.js b/lib/models/event.js
index 33ba03e72..92a9a5398 100644
--- a/lib/models/event.js
+++ b/lib/models/event.js
@@ -248,13 +248,25 @@ module.exports.MatrixEvent.prototype = {
      * Update the content of an event in the same way it would be by the server
      * if it were redacted before it was sent to us
      *
-     * @param {Object} the raw event causing the redaction
+     * @param {module:models/event.MatrixEvent} redaction_event
+     *     event causing the redaction
      */
     makeRedacted: function(redaction_event) {
+        // quick sanity-check
+        if (!redaction_event.event) {
+            throw new Error("invalid redaction_event in makeRedacted");
+        }
+
+        // we attempt to replicate what we would see from the server if
+        // the event had been redacted before we saw it.
+        //
+        // The server removes (most of) the content of the event, and adds a
+        // "redacted_because" key to the unsigned section containing the
+        // redacted event.
         if (!this.event.unsigned) {
             this.event.unsigned = {};
         }
-        this.event.unsigned.redacted_because = redaction_event;
+        this.event.unsigned.redacted_because = redaction_event.event;
 
         var key;
         for (key in this.event) {
diff --git a/spec/integ/matrix-client-event-timeline.spec.js b/spec/integ/matrix-client-event-timeline.spec.js
index db94541fb..6d77cd4d8 100644
--- a/spec/integ/matrix-client-event-timeline.spec.js
+++ b/spec/integ/matrix-client-event-timeline.spec.js
@@ -655,4 +655,70 @@ describe("MatrixClient event timelines", function() {
             }).catch(utils.failTest);
         });
     });
+
+
+    it("should handle gappy syncs after redactions", function(done) {
+        // https://github.com/vector-im/vector-web/issues/1389
+
+        // a state event, followed by a redaction thereof
+        var event = utils.mkMembership({
+            room: roomId, mship: "join", user: otherUserId
+        });
+        var redaction = utils.mkEvent({
+            type: "m.room.redaction",
+            room_id: roomId,
+            sender: otherUserId,
+            content: {}
+        });
+        redaction.redacts = event.event_id;
+
+        var syncData = {
+            next_batch: "batch1",
+            rooms: {
+                join: {},
+            },
+        };
+        syncData.rooms.join[roomId] = {
+            timeline: {
+                events: [
+                    event,
+                    redaction,
+                ],
+                limited: false,
+            },
+        };
+        httpBackend.when("GET", "/sync").respond(200, syncData);
+
+        httpBackend.flush().then(function() {
+            var room = client.getRoom(roomId);
+            var tl = room.getLiveTimeline();
+            expect(tl.getEvents().length).toEqual(3);
+            expect(tl.getEvents()[1].isRedacted()).toBe(true);
+
+            var sync2 = {
+                next_batch: "batch2",
+                rooms: {
+                    join: {},
+                },
+            };
+            sync2.rooms.join[roomId] = {
+                timeline: {
+                    events: [
+                        utils.mkMessage({
+                            room: roomId, user: otherUserId, msg: "world"
+                        }),
+                    ],
+                    limited: true,
+                    prev_batch: "newerTok",
+                },
+            };
+            httpBackend.when("GET", "/sync").respond(200, sync2);
+
+            return httpBackend.flush();
+        }).then(function() {
+            var room = client.getRoom(roomId);
+            var tl = room.getLiveTimeline();
+            expect(tl.getEvents().length).toEqual(1);
+        }).catch(utils.failTest).done(done);
+    });
 });
diff --git a/spec/test-utils.js b/spec/test-utils.js
index 39559187a..ecee27331 100644
--- a/spec/test-utils.js
+++ b/spec/test-utils.js
@@ -48,7 +48,7 @@ module.exports.mock = function(constr, name) {
  * @param {Object} opts Values for the event.
  * @param {string} opts.type The event.type
  * @param {string} opts.room The event.room_id
- * @param {string} opts.user The event.user_id
+ * @param {string} opts.sender The event.sender
  * @param {string} opts.skey Optional. The state key (auto inserts empty string)
  * @param {Object} opts.content The event.content
  * @param {boolean} opts.event True to make a MatrixEvent.
@@ -61,7 +61,7 @@ module.exports.mkEvent = function(opts) {
     var event = {
         type: opts.type,
         room_id: opts.room,
-        sender: opts.user,
+        sender: opts.sender || opts.user, // opts.user for backwards-compat
         content: opts.content,
         event_id: "$" + Math.random() + "-" + Math.random()
     };
@@ -88,7 +88,7 @@ module.exports.mkPresence = function(opts) {
     var event = {
         event_id: "$" + Math.random() + "-" + Math.random(),
         type: "m.presence",
-        sender: opts.user,
+        sender: opts.sender || opts.user, // opts.user for backwards-compat
         content: {
             avatar_url: opts.url,
             displayname: opts.name,
@@ -104,8 +104,8 @@ module.exports.mkPresence = function(opts) {
  * @param {Object} opts Values for the membership.
  * @param {string} opts.room The room ID for the event.
  * @param {string} opts.mship The content.membership for the event.
- * @param {string} opts.user The user ID for the event.
- * @param {string} opts.skey The other user ID for the event if applicable
+ * @param {string} opts.sender The sender user ID for the event.
+ * @param {string} opts.skey The target user ID for the event if applicable
  * e.g. for invites/bans.
  * @param {string} opts.name The content.displayname for the event.
  * @param {string} opts.url The content.avatar_url for the event.
@@ -115,7 +115,7 @@ module.exports.mkPresence = function(opts) {
 module.exports.mkMembership = function(opts) {
     opts.type = "m.room.member";
     if (!opts.skey) {
-        opts.skey = opts.user;
+        opts.skey = opts.sender || opts.user;
     }
     if (!opts.mship) {
         throw new Error("Missing .mship => " + JSON.stringify(opts));