diff --git a/spec/unit/models/poll.spec.ts b/spec/unit/models/poll.spec.ts
index 245d5646501..2acd405fbee 100644
--- a/spec/unit/models/poll.spec.ts
+++ b/spec/unit/models/poll.spec.ts
@@ -132,7 +132,7 @@ describe("Poll", () => {
         });
 
         it("filters relations for relevent response events", async () => {
-            const replyEvent = new MatrixEvent({ type: "m.room.message" });
+            const replyEvent = makeRelatedEvent({ type: "m.room.message" });
             const stableResponseEvent = makeRelatedEvent({ type: M_POLL_RESPONSE.stable! });
             const unstableResponseEvent = makeRelatedEvent({ type: M_POLL_RESPONSE.unstable });
 
@@ -188,6 +188,47 @@ describe("Poll", () => {
             });
         });
 
+        describe("undecryptable relations", () => {
+            it("counts undecryptable relation events when getting responses", async () => {
+                const replyEvent = makeRelatedEvent({ type: "m.room.message" });
+                const stableResponseEvent = makeRelatedEvent({ type: M_POLL_RESPONSE.stable! });
+                const undecryptableEvent = makeRelatedEvent({ type: M_POLL_RESPONSE.unstable });
+                jest.spyOn(undecryptableEvent, "isDecryptionFailure").mockReturnValue(true);
+
+                mockClient.relations.mockResolvedValue({
+                    events: [replyEvent, stableResponseEvent, undecryptableEvent],
+                });
+                const poll = new Poll(basePollStartEvent, mockClient, room);
+                jest.spyOn(poll, "emit");
+                await poll.getResponses();
+                expect(poll.undecryptableRelationsCount).toBe(1);
+                expect(poll.emit).toHaveBeenCalledWith(PollEvent.UndecryptableRelations, 1);
+            });
+
+            it("adds to undercryptable event count when new relation is undecryptable", async () => {
+                const replyEvent = makeRelatedEvent({ type: "m.room.message" });
+                const stableResponseEvent = makeRelatedEvent({ type: M_POLL_RESPONSE.stable! });
+                const undecryptableEvent = makeRelatedEvent({ type: M_POLL_RESPONSE.unstable });
+                const undecryptableEvent2 = makeRelatedEvent({ type: M_POLL_RESPONSE.unstable });
+                jest.spyOn(undecryptableEvent, "isDecryptionFailure").mockReturnValue(true);
+                jest.spyOn(undecryptableEvent2, "isDecryptionFailure").mockReturnValue(true);
+
+                mockClient.relations.mockResolvedValue({
+                    events: [replyEvent, stableResponseEvent, undecryptableEvent],
+                });
+                const poll = new Poll(basePollStartEvent, mockClient, room);
+                jest.spyOn(poll, "emit");
+                await poll.getResponses();
+                expect(poll.undecryptableRelationsCount).toBe(1);
+
+                await poll.onNewRelation(undecryptableEvent2);
+
+                expect(poll.undecryptableRelationsCount).toBe(2);
+
+                expect(poll.emit).toHaveBeenCalledWith(PollEvent.UndecryptableRelations, 2);
+            });
+        });
+
         describe("with poll end event", () => {
             const stablePollEndEvent = makeRelatedEvent({ type: M_POLL_END.stable!, sender: "@bob@server.org" });
             const unstablePollEndEvent = makeRelatedEvent({ type: M_POLL_END.unstable!, sender: "@bob@server.org" });
diff --git a/src/models/poll.ts b/src/models/poll.ts
index 8a080ef9015..1d4344a901c 100644
--- a/src/models/poll.ts
+++ b/src/models/poll.ts
@@ -28,6 +28,7 @@ export enum PollEvent {
     Update = "Poll.update",
     Responses = "Poll.Responses",
     Destroy = "Poll.Destroy",
+    UndecryptableRelations = "Poll.UndecryptableRelations",
 }
 
 export type PollEventHandlerMap = {
@@ -35,6 +36,7 @@ export type PollEventHandlerMap = {
     [PollEvent.Destroy]: (pollIdentifier: string) => void;
     [PollEvent.End]: () => void;
     [PollEvent.Responses]: (responses: Relations) => void;
+    [PollEvent.UndecryptableRelations]: (count: number) => void;
 };
 
 const filterResponseRelations = (
@@ -45,7 +47,6 @@ const filterResponseRelations = (
 } => {
     const responseEvents = relationEvents.filter((event) => {
         if (event.isDecryptionFailure()) {
-            // @TODO(kerrya) PSG-1023 track and return these
             return;
         }
         return (
@@ -66,6 +67,11 @@ export class Poll extends TypedEventEmitter<Exclude<PollEvent, PollEvent.New>, P
     private relationsNextBatch: string | undefined;
     private responses: null | Relations = null;
     private endEvent: MatrixEvent | undefined;
+    /**
+     * Keep track of undecryptable relations
+     * As incomplete result sets affect poll results
+     */
+    private undecryptableRelationEventIds = new Set<string>();
 
     public constructor(public readonly rootEvent: MatrixEvent, private matrixClient: MatrixClient, private room: Room) {
         super();
@@ -80,6 +86,10 @@ export class Poll extends TypedEventEmitter<Exclude<PollEvent, PollEvent.New>, P
         return this.rootEvent.getId()!;
     }
 
+    public get endEventId(): string | undefined {
+        return this.endEvent?.getId();
+    }
+
     public get isEnded(): boolean {
         return !!this.endEvent;
     }
@@ -88,6 +98,10 @@ export class Poll extends TypedEventEmitter<Exclude<PollEvent, PollEvent.New>, P
         return this._isFetchingResponses;
     }
 
+    public get undecryptableRelationsCount(): number {
+        return this.undecryptableRelationEventIds.size;
+    }
+
     public async getResponses(): Promise<Relations> {
         // if we have already fetched some responses
         // just return them
@@ -124,10 +138,13 @@ export class Poll extends TypedEventEmitter<Exclude<PollEvent, PollEvent.New>, P
         const pollEndTimestamp = this.endEvent?.getTs() || Number.MAX_SAFE_INTEGER;
         const { responseEvents } = filterResponseRelations([event], pollEndTimestamp);
 
+        this.countUndecryptableEvents([event]);
+
         if (responseEvents.length) {
             responseEvents.forEach((event) => {
                 this.responses!.addEvent(event);
             });
+
             this.emit(PollEvent.Responses, this.responses);
         }
     }
@@ -173,6 +190,7 @@ export class Poll extends TypedEventEmitter<Exclude<PollEvent, PollEvent.New>, P
 
         this.relationsNextBatch = allRelations.nextBatch ?? undefined;
         this.responses = responses;
+        this.countUndecryptableEvents(allRelations.events);
 
         // while there are more pages of relations
         // fetch them
@@ -209,6 +227,19 @@ export class Poll extends TypedEventEmitter<Exclude<PollEvent, PollEvent.New>, P
         this.emit(PollEvent.Responses, this.responses);
     }
 
+    private countUndecryptableEvents = (events: MatrixEvent[]): void => {
+        const undecryptableEventIds = events
+            .filter((event) => event.isDecryptionFailure())
+            .map((event) => event.getId()!);
+
+        const previousCount = this.undecryptableRelationsCount;
+        this.undecryptableRelationEventIds = new Set([...this.undecryptableRelationEventIds, ...undecryptableEventIds]);
+
+        if (this.undecryptableRelationsCount !== previousCount) {
+            this.emit(PollEvent.UndecryptableRelations, this.undecryptableRelationsCount);
+        }
+    };
+
     private validateEndEvent(endEvent?: MatrixEvent): boolean {
         if (!endEvent) {
             return false;