diff --git a/package.json b/package.json
index 510b96aa0189..ecf2de39d3dc 100644
--- a/package.json
+++ b/package.json
@@ -21,7 +21,7 @@
 		"build-assets": "node ./scripts/build-assets.mjs",
 		"build": "pnpm build-pre && pnpm -r build && pnpm build-assets",
 		"build-storybook": "pnpm --filter frontend build-storybook",
-		"build-misskey-js-with-types": "pnpm build-pre && pnpm --filter backend... --filter=!misskey-js build && pnpm --filter backend generate-api-json && ncp packages/backend/built/api.json packages/misskey-js/generator/api.json && pnpm --filter misskey-js update-autogen-code && pnpm --filter misskey-js build && pnpm --filter misskey-js api",
+		"build-misskey-js-with-types": "pnpm build-pre && pnpm --filter backend... --filter=!misskey-js build && pnpm --filter backend generate-api-json --no-build && ncp packages/backend/built/api.json packages/misskey-js/generator/api.json && pnpm --filter misskey-js update-autogen-code && pnpm --filter misskey-js build && pnpm --filter misskey-js api",
 		"start": "pnpm check:connect && cd packages/backend && node ./built/boot/entry.js",
 		"start:test": "cd packages/backend && cross-env NODE_ENV=test node ./built/boot/entry.js",
 		"init": "pnpm migrate",
diff --git a/packages/backend/package.json b/packages/backend/package.json
index 22fdc5cf1681..b99717d15cea 100644
--- a/packages/backend/package.json
+++ b/packages/backend/package.json
@@ -31,7 +31,7 @@
 		"test:e2e": "pnpm build && pnpm build:test && pnpm jest:e2e",
 		"test-and-coverage": "pnpm jest-and-coverage",
 		"test-and-coverage:e2e": "pnpm build && pnpm build:test && pnpm jest-and-coverage:e2e",
-		"generate-api-json": "pnpm build && node ./scripts/generate_api_json.js"
+		"generate-api-json": "node ./scripts/generate_api_json.js"
 	},
 	"optionalDependencies": {
 		"@swc/core-android-arm64": "1.3.11",
diff --git a/packages/backend/scripts/generate_api_json.js b/packages/backend/scripts/generate_api_json.js
index b4769ef8012e..798e2430040a 100644
--- a/packages/backend/scripts/generate_api_json.js
+++ b/packages/backend/scripts/generate_api_json.js
@@ -3,11 +3,34 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-import { loadConfig } from '../built/config.js'
-import { genOpenapiSpec } from '../built/server/api/openapi/gen-spec.js'
-import { writeFileSync } from "node:fs";
+import { execa } from 'execa';
+import { writeFileSync, existsSync } from "node:fs";
 
-const config = loadConfig();
-const spec = genOpenapiSpec(config, true);
+async function main() {
+	if (!process.argv.includes('--no-build')) {
+		await execa('pnpm', ['run', 'build'], {
+			stdout: process.stdout,
+			stderr: process.stderr,
+		});
+	}
 
-writeFileSync('./built/api.json', JSON.stringify(spec), 'utf-8');
+	if (!existsSync('./built')) {
+		throw new Error('`built` directory does not exist.');
+	}
+
+	/** @type {import('../src/config.js')} */
+	const { loadConfig } = await import('../built/config.js');
+
+	/** @type {import('../src/server/api/openapi/gen-spec.js')} */
+	const { genOpenapiSpec } = await import('../built/server/api/openapi/gen-spec.js');
+
+	const config = loadConfig();
+	const spec = genOpenapiSpec(config, true);
+
+	writeFileSync('./built/api.json', JSON.stringify(spec), 'utf-8');
+}
+
+main().catch(e => {
+	console.error(e);
+	process.exit(1);
+});