diff --git a/src/app.ts b/src/app.ts
index ccca7a83..4b0a8bba 100644
--- a/src/app.ts
+++ b/src/app.ts
@@ -165,18 +165,24 @@ if (process.env.USE_MQ === 'true') {
     logging.info('Message queue is enabled');
 
     try {
+        const host = String(process.env.MQ_PUBSUB_HOST) || undefined;
+        const emulatorMode = process.env.NODE_ENV !== 'production';
+        const projectId = String(process.env.MQ_PUBSUB_PROJECT_ID) || undefined;
+        const topicName = String(process.env.MQ_PUBSUB_TOPIC_NAME);
+        const subscriptionName = String(
+            process.env.MQ_PUBSUB_SUBSCRIPTION_NAME,
+        );
+
         queue = await initGCloudPubSubMessageQueue(
             logging,
             eventBus,
             EVENT_MQ_MESSAGE_RECEIVED,
             {
-                host: String(process.env.MQ_PUBSUB_HOST),
-                emulatorMode: process.env.NODE_ENV !== 'production',
-                projectId: String(process.env.MQ_PUBSUB_PROJECT_ID),
-                topicName: String(process.env.MQ_PUBSUB_TOPIC_NAME),
-                subscriptionName: String(
-                    process.env.MQ_PUBSUB_SUBSCRIPTION_NAME,
-                ),
+                host,
+                emulatorMode,
+                projectId,
+                topicName,
+                subscriptionName,
             },
         );
     } catch (err) {
diff --git a/src/helpers/gcloud-pubsub-mq.ts b/src/helpers/gcloud-pubsub-mq.ts
index 319b69ef..1b649279 100644
--- a/src/helpers/gcloud-pubsub-mq.ts
+++ b/src/helpers/gcloud-pubsub-mq.ts
@@ -1,5 +1,5 @@
 import type { EventEmitter } from 'node:events';
-import { PubSub } from '@google-cloud/pubsub';
+import { type ClientConfig, PubSub } from '@google-cloud/pubsub';
 import type { Logger } from '@logtape/logtape';
 
 import { GCloudPubSubMessageQueue } from '../mq/gcloud-pubsub-mq';
@@ -36,9 +36,9 @@ async function subscriptionExists(
 }
 
 type InitGCloudPubSubMessageQueueOptions = {
-    host: string;
-    emulatorMode: boolean;
-    projectId: string;
+    host?: string;
+    emulatorMode?: boolean;
+    projectId?: string;
     topicName: string;
     subscriptionName: string;
 };
@@ -55,15 +55,28 @@ export async function initGCloudPubSubMessageQueue(
         subscriptionName = 'unknown_subscription',
     }: InitGCloudPubSubMessageQueueOptions,
 ) {
-    const pubSubClient = new PubSub({
-        projectId,
-        apiEndpoint: host,
-        emulatorMode,
-    });
+    const pubsubClientConfig: Partial<ClientConfig> = {};
+
+    if (host !== undefined) {
+        pubsubClientConfig.apiEndpoint = host;
+    }
+
+    if (emulatorMode !== undefined) {
+        pubsubClientConfig.emulatorMode = emulatorMode;
+    }
 
-    const topicIdentifier = getFullTopicIdentifier(projectId, topicName);
+    if (projectId !== undefined) {
+        pubsubClientConfig.projectId = projectId;
+    }
+
+    const pubSubClient = new PubSub(pubsubClientConfig);
+
+    const topicIdentifier = getFullTopicIdentifier(
+        pubSubClient.projectId,
+        topicName,
+    );
     const subscriptionIdentifier = getFullSubscriptionIdentifier(
-        projectId,
+        pubSubClient.projectId,
         subscriptionName,
     );
 
diff --git a/src/helpers/gcloud-pubsub-mq.unit.test.ts b/src/helpers/gcloud-pubsub-mq.unit.test.ts
index 02669bbf..11ba3176 100644
--- a/src/helpers/gcloud-pubsub-mq.unit.test.ts
+++ b/src/helpers/gcloud-pubsub-mq.unit.test.ts
@@ -69,6 +69,7 @@ describe('initGCloudPubSubMessageQueue', () => {
             return {
                 getTopics: vi.fn().mockResolvedValue([topics]),
                 getSubscriptions: vi.fn().mockResolvedValue([subscriptions]),
+                projectId: options.projectId,
             };
         });
 
@@ -100,6 +101,55 @@ describe('initGCloudPubSubMessageQueue', () => {
         );
     });
 
+    it('should only explicitly provide options to the PubSub client if they are defined', async () => {
+        const projectId = 'foo';
+        const options = {
+            topicName: 'baz',
+            subscriptionName: 'qux',
+        };
+        const topics: Topic[] = [
+            {
+                name: getFullTopicIdentifier(projectId, options.topicName),
+            } as Topic,
+        ];
+        const subscriptions: Subscription[] = [
+            {
+                name: getFullSubscriptionIdentifier(
+                    projectId,
+                    options.subscriptionName,
+                ),
+            } as Subscription,
+        ];
+
+        (vi.mocked(PubSub) as Mock).mockImplementation(() => {
+            return {
+                getTopics: vi.fn().mockResolvedValue([topics]),
+                getSubscriptions: vi.fn().mockResolvedValue([subscriptions]),
+                projectId,
+            };
+        });
+
+        await expect(
+            initGCloudPubSubMessageQueue(
+                mockLogger,
+                mockEventBus,
+                EVENT_NAME,
+                options,
+            ),
+        ).resolves.toBeInstanceOf(GCloudPubSubMessageQueue);
+
+        expect(PubSub).toHaveBeenCalledWith({});
+
+        expect(GCloudPubSubMessageQueue).toHaveBeenCalledWith(
+            expect.any(Object),
+            mockEventBus,
+            mockLogger,
+            getFullTopicIdentifier(projectId, options.topicName),
+            getFullSubscriptionIdentifier(projectId, options.subscriptionName),
+            EVENT_NAME,
+        );
+    });
+
     it('should throw an error if the topic does not exist', async () => {
         const options = {
             host: 'foo',
@@ -113,6 +163,7 @@ describe('initGCloudPubSubMessageQueue', () => {
         (vi.mocked(PubSub) as Mock).mockImplementation(() => {
             return {
                 getTopics: vi.fn().mockResolvedValue([topics]),
+                projectId: options.projectId,
             };
         });
 
@@ -148,6 +199,7 @@ describe('initGCloudPubSubMessageQueue', () => {
             return {
                 getTopics: vi.fn().mockResolvedValue([topics]),
                 getSubscriptions: vi.fn().mockResolvedValue([subscriptions]),
+                projectId: options.projectId,
             };
         });