diff --git a/cypress/tsconfig.json b/cypress/tsconfig.json
index e61061f41c..fb434b9a41 100644
--- a/cypress/tsconfig.json
+++ b/cypress/tsconfig.json
@@ -1,7 +1,7 @@
 {
 	"compilerOptions": {
-		"lib": ["dom", "ES2022"],
-		"target": "ES2022",
+		"lib": ["dom", "ESNext"],
+		"target": "ESNext",
 		"types": ["cypress", "node"],
 		"incremental": true,
 		"skipLibCheck": true,
diff --git a/packages/backend/src/core/HttpRequestService.ts b/packages/backend/src/core/HttpRequestService.ts
index 3b3e72d2e3..8000f1fd6c 100644
--- a/packages/backend/src/core/HttpRequestService.ts
+++ b/packages/backend/src/core/HttpRequestService.ts
@@ -73,7 +73,7 @@ export function validateSocketConnect(allowedPrivateNetworks: PrivateNetwork[] |
 
 declare module 'node:http' {
 	interface Agent {
-		createConnection(options: net.NetConnectOpts, callback?: (err: unknown, stream: net.Socket) => void): net.Socket;
+		createConnection(options: net.NetConnectOpts, callback?: (err: Error | null, stream: net.Socket) => void): net.Socket;
 	}
 }
 
@@ -86,7 +86,7 @@ class HttpRequestServiceAgent extends http.Agent {
 	}
 
 	@bindThis
-	public createConnection(options: net.NetConnectOpts, callback?: (err: unknown, stream: net.Socket) => void): net.Socket {
+	public createConnection(options: net.NetConnectOpts, callback?: (err: Error | null, stream: net.Socket) => void): net.Socket {
 		const socket = super.createConnection(options, callback)
 			.on('connect', () => {
 				if (process.env.NODE_ENV === 'production') {
@@ -106,7 +106,7 @@ class HttpsRequestServiceAgent extends https.Agent {
 	}
 
 	@bindThis
-	public createConnection(options: net.NetConnectOpts, callback?: (err: unknown, stream: net.Socket) => void): net.Socket {
+	public createConnection(options: net.NetConnectOpts, callback?: (err: Error | null, stream: net.Socket) => void): net.Socket {
 		const socket = super.createConnection(options, callback)
 			.on('connect', () => {
 				if (process.env.NODE_ENV === 'production') {
diff --git a/packages/backend/src/core/QueueService.ts b/packages/backend/src/core/QueueService.ts
index 486af69f3a..07ee8f3931 100644
--- a/packages/backend/src/core/QueueService.ts
+++ b/packages/backend/src/core/QueueService.ts
@@ -896,7 +896,7 @@ export class QueueService implements OnModuleInit {
 	@bindThis
 	public async queueRetryJob(queueType: typeof QUEUE_TYPES[number], jobId: string) {
 		const queue = this.getQueue(queueType);
-		const job: Bull.Job | null = await queue.getJob(jobId);
+		const job: Bull.Job | undefined = await queue.getJob(jobId);
 		if (job) {
 			if (job.finishedOn != null) {
 				await job.retry();
@@ -909,7 +909,7 @@ export class QueueService implements OnModuleInit {
 	@bindThis
 	public async queueRemoveJob(queueType: typeof QUEUE_TYPES[number], jobId: string) {
 		const queue = this.getQueue(queueType);
-		const job: Bull.Job | null = await queue.getJob(jobId);
+		const job: Bull.Job | undefined = await queue.getJob(jobId);
 		if (job) {
 			await job.remove();
 		}
@@ -943,7 +943,7 @@ export class QueueService implements OnModuleInit {
 	@bindThis
 	public async queueGetJob(queueType: typeof QUEUE_TYPES[number], jobId: string) {
 		const queue = this.getQueue(queueType);
-		const job: Bull.Job | null = await queue.getJob(jobId);
+		const job: Bull.Job | undefined = await queue.getJob(jobId);
 		if (job) {
 			return this.packJobData(job);
 		} else {
diff --git a/packages/backend/src/server/api/mastodon/MastodonLogger.ts b/packages/backend/src/server/api/mastodon/MastodonLogger.ts
index 5ea69ed151..dda9fcfd6b 100644
--- a/packages/backend/src/server/api/mastodon/MastodonLogger.ts
+++ b/packages/backend/src/server/api/mastodon/MastodonLogger.ts
@@ -67,7 +67,7 @@ export function getErrorException(error: unknown): Error | null {
 		}
 
 		// This is the inner exception, basically
-		if (error.cause && !isAxiosError(error.cause)) {
+		if (error.cause instanceof Error && !isAxiosError(error.cause)) {
 			if (!error.cause.stack) {
 				error.cause.stack = error.stack;
 			}
@@ -150,7 +150,7 @@ function unpackAxiosError(error: unknown): unknown {
 			return undefined;
 		}
 
-		if (error.cause && !isAxiosError(error.cause)) {
+		if (error.cause instanceof Error && !isAxiosError(error.cause)) {
 			if (!error.cause.stack) {
 				error.cause.stack = error.stack;
 			}
diff --git a/packages/backend/test-federation/test/utils.ts b/packages/backend/test-federation/test/utils.ts
index b155103efa..62ed1ce518 100644
--- a/packages/backend/test-federation/test/utils.ts
+++ b/packages/backend/test-federation/test/utils.ts
@@ -196,7 +196,7 @@ export async function uploadFile(
 	body.append('name', filename);
 
 	return await fetch(`https://${host}/api/drive/files/create`, { method: 'POST', body })
-		.then(async res => await res.json());
+		.then(async res => await res.json() as Misskey.entities.DriveFile);
 }
 
 export async function addCustomEmoji(
diff --git a/packages/backend/test-federation/tsconfig.json b/packages/backend/test-federation/tsconfig.json
index df2d4bb97d..40fbfa3bb0 100644
--- a/packages/backend/test-federation/tsconfig.json
+++ b/packages/backend/test-federation/tsconfig.json
@@ -11,8 +11,8 @@
 		// "disableReferencedProjectLoad": true,             /* Reduce the number of projects loaded automatically by TypeScript. */
 
 		/* Language and Environment */
-		"target": "ES2022",                                  /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */
-		// "lib": [],                                        /* Specify a set of bundled library declaration files that describe the target runtime environment. */
+		"target": "ESNext",                                  /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */
+		"lib": ["ESNext"],                                        /* Specify a set of bundled library declaration files that describe the target runtime environment. */
 		// "jsx": "preserve",                                /* Specify what JSX code is generated. */
 		// "experimentalDecorators": true,                   /* Enable experimental support for legacy experimental decorators. */
 		// "emitDecoratorMetadata": true,                    /* Emit design-type metadata for decorated declarations in source files. */