diff --git a/packages/framework/presence/src/test/presenceDatastoreManager.spec.ts b/packages/framework/presence/src/test/presenceDatastoreManager.spec.ts
index 7c1d0d1cfa9e..043e1bee8339 100644
--- a/packages/framework/presence/src/test/presenceDatastoreManager.spec.ts
+++ b/packages/framework/presence/src/test/presenceDatastoreManager.spec.ts
@@ -5,12 +5,18 @@
 
 import { strict as assert } from "node:assert";
 
+import type {
+	InboundExtensionMessage,
+	RawInboundExtensionMessage,
+} from "@fluidframework/container-runtime-definitions/internal";
+import { validateAssertionError } from "@fluidframework/test-runtime-utils/internal";
 import { EventAndErrorTrackingLogger } from "@fluidframework/test-utils/internal";
 import type { SinonFakeTimers } from "sinon";
 import { useFakeTimers, spy } from "sinon";
 
 import type { AttendeeId } from "../presence.js";
 import { createPresenceManager } from "../presenceManager.js";
+import type { SignalMessages } from "../protocol.js";
 import type { SystemWorkspaceDatastore } from "../systemWorkspace.js";
 
 import { MockEphemeralRuntime } from "./mockEphemeralRuntime.js";
@@ -472,5 +478,102 @@ describe("Presence", () => {
 				assert.strictEqual(listener.callCount, 1);
 			});
 		});
+
+		describe("receiving unrecognized message", () => {
+			let presence: ReturnType<typeof createPresenceManager>;
+
+			const systemWorkspaceUpdate = {
+				"clientToSessionId": {
+					"client1": {
+						"rev": 0,
+						"timestamp": 0,
+						"value": attendeeId1,
+					},
+				},
+			};
+
+			const statesWorkspaceUpdate = {
+				"latest": {
+					[attendeeId1]: {
+						"rev": 1,
+						"timestamp": 0,
+						"value": {},
+					},
+				},
+			};
+
+			beforeEach(() => {
+				presence = prepareConnectedPresence(
+					runtime,
+					attendeeId2,
+					connectionId2,
+					clock,
+					logger,
+				);
+
+				// Pass a little time (to mimic reality)
+				clock.tick(10);
+			});
+
+			/**
+			 * Use to pretend any general inbound message is an unverified Presence message
+			 */
+			function markUnverifiedIncomingMessage(
+				message: InboundExtensionMessage,
+			): RawInboundExtensionMessage<SignalMessages> {
+				return message as RawInboundExtensionMessage<SignalMessages>;
+			}
+
+			function processUnrecognizedMessage({ optional }: { optional: boolean }): void {
+				// Mocked to look very much like a Presence message, but with an unrecognized type.
+				const unrecognizedMessage = {
+					type: "Pres: Unrecognized Message",
+					content: {
+						sendTimestamp: clock.now - 10,
+						avgLatency: 20,
+						data: {
+							"system:presence": systemWorkspaceUpdate,
+							"s:name:testStateWorkspace": statesWorkspaceUpdate,
+						},
+					},
+					clientId: "client1",
+				} as const satisfies Omit<InboundExtensionMessage<SignalMessages>, "type"> & {
+					type: string;
+				};
+				presence.processSignal(
+					optional ? ["?"] : [],
+					markUnverifiedIncomingMessage(unrecognizedMessage),
+					false,
+				);
+			}
+
+			it("that is NOT optional, throws", () => {
+				// Setup
+				const listener = spy();
+				presence.events.on("workspaceActivated", listener);
+
+				// Act & Verify
+				assert.throws(
+					() => processUnrecognizedMessage({ optional: false }),
+					(e: Error) =>
+						validateAssertionError(e, /Unrecognized message type in critical message/),
+				);
+
+				// Verify
+				assert.strictEqual(listener.called, false);
+			});
+
+			it("that is optional, ignores message and does NOT throw", () => {
+				// Setup
+				const listener = spy();
+				presence.events.on("workspaceActivated", listener);
+
+				// Act & Verify
+				processUnrecognizedMessage({ optional: true });
+
+				// Verify
+				assert.strictEqual(listener.called, false);
+			});
+		});
 	});
 });