diff --git a/frontend/src/lib/document/viewer/usePdfRenderer.svelte.test.ts b/frontend/src/lib/document/viewer/usePdfRenderer.svelte.test.ts
index 9d56d95c..7bdf387d 100644
--- a/frontend/src/lib/document/viewer/usePdfRenderer.svelte.test.ts
+++ b/frontend/src/lib/document/viewer/usePdfRenderer.svelte.test.ts
@@ -193,4 +193,17 @@ describe('createPdfRenderer', () => {
 		await expect(r.init()).rejects.toThrow('load failed');
 		expect(r.pdfjsReady).toBe(false);
 	});
+
+	it('init() is idempotent — libLoader called only once on repeated calls', async () => {
+		const fakePdfjs = {
+			GlobalWorkerOptions: { workerSrc: '' },
+			getDocument: vi.fn(),
+			TextLayer: class {}
+		} as unknown as typeof import('pdfjs-dist');
+		const fakeLoader = vi.fn().mockResolvedValue([fakePdfjs, { default: '' }] as const);
+		const r = createPdfRenderer(fakeLoader);
+		await r.init();
+		await r.init();
+		expect(fakeLoader).toHaveBeenCalledOnce();
+	});
 });
diff --git a/frontend/src/lib/document/viewer/usePdfRenderer.svelte.ts b/frontend/src/lib/document/viewer/usePdfRenderer.svelte.ts
index 700984e9..13315f8e 100644
--- a/frontend/src/lib/document/viewer/usePdfRenderer.svelte.ts
+++ b/frontend/src/lib/document/viewer/usePdfRenderer.svelte.ts
@@ -23,6 +23,7 @@ export function createPdfRenderer(libLoader: LibLoader = defaultLibLoader) {
 	let pdfjsLib: typeof import('pdfjs-dist') | null = null;
 
 	async function init(): Promise<void> {
+		if (pdfjsReady) return;
 		const [lib, { default: workerUrl }] = await libLoader();
 		lib.GlobalWorkerOptions.workerSrc = workerUrl;
 		pdfjsLib = lib;