diff --git a/spec/unit/matrixrtc/CallMembership.spec.ts b/spec/unit/matrixrtc/CallMembership.spec.ts
index a8ae0a822..6f7f8f5ca 100644
--- a/spec/unit/matrixrtc/CallMembership.spec.ts
+++ b/spec/unit/matrixrtc/CallMembership.spec.ts
@@ -23,6 +23,7 @@ const membershipTemplate: CallMembershipData = {
     application: "m.call",
     device_id: "AAAAAAA",
     expires: 5000,
+    membershipID: "bloop",
 };
 
 function makeMockEvent(originTs = 0): MatrixEvent {
diff --git a/spec/unit/matrixrtc/MatrixRTCSession.spec.ts b/spec/unit/matrixrtc/MatrixRTCSession.spec.ts
index 9572e1f8b..f8c229c9a 100644
--- a/spec/unit/matrixrtc/MatrixRTCSession.spec.ts
+++ b/spec/unit/matrixrtc/MatrixRTCSession.spec.ts
@@ -26,6 +26,7 @@ const membershipTemplate: CallMembershipData = {
     application: "m.call",
     device_id: "AAAAAAA",
     expires: 60 * 60 * 1000,
+    membershipID: "bloop",
 };
 
 const mockFocus = { type: "mock" };
@@ -56,6 +57,7 @@ describe("MatrixRTCSession", () => {
         expect(sess?.memberships[0].scope).toEqual("m.room");
         expect(sess?.memberships[0].application).toEqual("m.call");
         expect(sess?.memberships[0].deviceId).toEqual("AAAAAAA");
+        expect(sess?.memberships[0].membershipID).toEqual("bloop");
         expect(sess?.memberships[0].isExpired()).toEqual(false);
     });
 
@@ -219,6 +221,7 @@ describe("MatrixRTCSession", () => {
                             device_id: "AAAAAAA",
                             expires: 3600000,
                             foci_active: [{ type: "mock" }],
+                            membershipID: expect.stringMatching(".*"),
                         },
                     ],
                 },
@@ -286,6 +289,7 @@ describe("MatrixRTCSession", () => {
                                 expires: 3600000 * 2,
                                 foci_active: [{ type: "mock" }],
                                 created_ts: 1000,
+                                membershipID: expect.stringMatching(".*"),
                             },
                         ],
                     },
@@ -357,6 +361,7 @@ describe("MatrixRTCSession", () => {
                         device_id: "AAAAAAA",
                         expires: 3600000,
                         foci_active: [mockFocus],
+                        membershipID: expect.stringMatching(".*"),
                     },
                 ],
             },
@@ -388,6 +393,7 @@ describe("MatrixRTCSession", () => {
                         device_id: "OTHERDEVICE",
                         expires: 3600000,
                         created_ts: 1000,
+                        membershipID: expect.stringMatching(".*"),
                     },
                     {
                         application: "m.call",
@@ -396,6 +402,7 @@ describe("MatrixRTCSession", () => {
                         device_id: "AAAAAAA",
                         expires: 3600000,
                         foci_active: [mockFocus],
+                        membershipID: expect.stringMatching(".*"),
                     },
                 ],
             },
diff --git a/spec/unit/matrixrtc/MatrixRTCSessionManager.spec.ts b/spec/unit/matrixrtc/MatrixRTCSessionManager.spec.ts
index fb96c3e53..6a240831e 100644
--- a/spec/unit/matrixrtc/MatrixRTCSessionManager.spec.ts
+++ b/spec/unit/matrixrtc/MatrixRTCSessionManager.spec.ts
@@ -26,6 +26,7 @@ const membershipTemplate: CallMembershipData = {
     application: "m.call",
     device_id: "AAAAAAA",
     expires: 60 * 60 * 1000,
+    membershipID: "bloop",
 };
 
 describe("MatrixRTCSessionManager", () => {
diff --git a/src/matrixrtc/CallMembership.ts b/src/matrixrtc/CallMembership.ts
index e67909d1e..b73a937b9 100644
--- a/src/matrixrtc/CallMembership.ts
+++ b/src/matrixrtc/CallMembership.ts
@@ -29,6 +29,7 @@ export interface CallMembershipData {
     created_ts?: number;
     expires: number;
     foci_active?: Focus[];
+    membershipID: string;
 }
 
 export class CallMembership {
@@ -64,6 +65,10 @@ export class CallMembership {
         return this.data.scope;
     }
 
+    public get membershipID(): string {
+        return this.data.membershipID;
+    }
+
     public createdTs(): number {
         return this.data.created_ts ?? this.parentEvent.getTs();
     }
diff --git a/src/matrixrtc/MatrixRTCSession.ts b/src/matrixrtc/MatrixRTCSession.ts
index 5f9ce7cc5..fc3d63cc6 100644
--- a/src/matrixrtc/MatrixRTCSession.ts
+++ b/src/matrixrtc/MatrixRTCSession.ts
@@ -23,6 +23,7 @@ import { EventType } from "../@types/event";
 import { CallMembership, CallMembershipData } from "./CallMembership";
 import { Focus } from "./focus";
 import { MatrixEvent } from "../matrix";
+import { randomString } from "../randomstring";
 
 const MEMBERSHIP_EXPIRY_TIME = 60 * 60 * 1000;
 const MEMBER_EVENT_CHECK_PERIOD = 2 * 60 * 1000; // How often we check to see if we need to re-send our member event
@@ -54,6 +55,14 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
     // if we're not yet joined
     private relativeExpiry: number | undefined;
 
+    // An identifier for our membership of the call. This will allow us to easily recognise
+    // whether a membership was sent by this session or is stale from some other time.
+    // It also forces our membership events to be unique, because otherwise we could try
+    // to overwrite a membership from a previous session but it would do nothing because the
+    // event content would be identical. We need the origin_server_ts to update though, so
+    // forcing unique content fixes this.
+    private membershipId: string | undefined;
+
     private memberEventTimeout?: ReturnType<typeof setTimeout>;
     private expiryTimeout?: ReturnType<typeof setTimeout>;
 
@@ -174,6 +183,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
         logger.info(`Joining call session in room ${this.room.roomId}`);
         this.activeFoci = activeFoci;
         this.relativeExpiry = MEMBERSHIP_EXPIRY_TIME;
+        this.membershipId = randomString(5);
         this.emit(MatrixRTCSessionEvent.JoinStateChanged, true);
         // We don't wait for this, mostly because it may fail and schedule a retry, so this
         // function returning doesn't really mean anything at all.
@@ -195,6 +205,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
         logger.info(`Leaving call session in room ${this.room.roomId}`);
         this.relativeExpiry = undefined;
         this.activeFoci = undefined;
+        this.membershipId = undefined;
         this.emit(MatrixRTCSessionEvent.JoinStateChanged, false);
         this.triggerCallMembershipEventUpdate();
     }
@@ -249,6 +260,9 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
         if (this.relativeExpiry === undefined) {
             throw new Error("Tried to create our own membership event when we're not joined!");
         }
+        if (this.membershipId === undefined) {
+            throw new Error("Tried to create our own membership event when we have no membership ID!");
+        }
 
         const m: CallMembershipData = {
             call_id: "",
@@ -257,6 +271,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
             device_id: this.client.getDeviceId()!,
             expires: this.relativeExpiry,
             foci_active: this.activeFoci,
+            membershipID: this.membershipId,
         };
 
         if (prevMembership) m.created_ts = prevMembership.createdTs();
@@ -373,7 +388,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
         const myPrevMembershipData = memberships.find((m) => m.device_id === localDeviceId);
         let myPrevMembership;
         try {
-            if (myCallMemberEvent && myPrevMembershipData) {
+            if (myCallMemberEvent && myPrevMembershipData && myPrevMembershipData.membershipID === this.membershipId) {
                 myPrevMembership = new CallMembership(myCallMemberEvent, myPrevMembershipData);
             }
         } catch (e) {