diff --git a/lib/upload/uploader/Uploader.spec.ts b/lib/upload/uploader/Uploader.spec.ts
index f9926c40..309dde38 100644
--- a/lib/upload/uploader/Uploader.spec.ts
+++ b/lib/upload/uploader/Uploader.spec.ts
@@ -60,11 +60,20 @@ vi.mock('./UploadFile.ts', () => ({
 		removeEventListener() {}
 		dispatchEvent = (() => true) as any
 		dispatchTypedEvent = (() => true) as any
-		cancel = vi.fn(() => {
+
+		// Mirrors the real `Upload.cancel`: a method that accesses private state,
+		// so calling it with a foreign `this` throws instead of silently working.
+		#cancelled = false
+		get cancelled(): boolean {
+			return this.#cancelled
+		}
+
+		cancel() {
+			this.#cancelled = true
 			if (this.status !== UploadStatus.FINISHED) {
 				this.status = UploadStatus.CANCELLED
 			}
-		})
+		}
 
 		start = async () => {
 			// simulate progress then finish
@@ -107,11 +116,20 @@ vi.mock('./UploadFileTree.ts', () => ({
 		removeEventListener = (() => {}) as any
 		dispatchEvent = (() => true) as any
 		dispatchTypedEvent = (() => true) as any
-		cancel = vi.fn(() => {
+
+		// Mirrors the real `Upload.cancel`: a method that accesses private state,
+		// so calling it with a foreign `this` throws instead of silently working.
+		#cancelled = false
+		get cancelled(): boolean {
+			return this.#cancelled
+		}
+
+		cancel() {
+			this.#cancelled = true
 			if (this.status !== UploadStatus.FINISHED) {
 				this.status = UploadStatus.CANCELLED as TUploadStatus
 			}
-		})
+		}
 
 		initialize = () => []
 		start = async () => {
@@ -250,6 +268,49 @@ describe('Uploader (current API)', () => {
 		expect(finished).toHaveBeenCalled()
 	})
 
+	describe('abort signal', () => {
+		it('cancels a single upload when the signal is aborted', async () => {
+			const uploader = new Uploader()
+			const controller = new AbortController()
+
+			const upload = await uploader.upload('/hello.txt', new File(['a'], 'hello.txt'), { signal: controller.signal })
+			expect((upload as unknown as { cancelled: boolean }).cancelled).toBe(false)
+
+			controller.abort()
+			expect((upload as unknown as { cancelled: boolean }).cancelled).toBe(true)
+		})
+
+		it('cancels a batch upload when the signal is aborted', async () => {
+			const uploader = new Uploader()
+			const controller = new AbortController()
+
+			const uploads = await uploader.batchUpload('/dir', [new File(['a'], 'a.txt')], { signal: controller.signal })
+			const root = uploads.at(-1) as unknown as { cancelled: boolean }
+			expect(root.cancelled).toBe(false)
+
+			controller.abort()
+			expect(root.cancelled).toBe(true)
+		})
+
+		it('cancels a single upload when the signal is already aborted', async () => {
+			const uploader = new Uploader()
+			const controller = new AbortController()
+			controller.abort()
+
+			const upload = await uploader.upload('/hello.txt', new File(['a'], 'hello.txt'), { signal: controller.signal })
+			expect((upload as unknown as { cancelled: boolean }).cancelled).toBe(true)
+		})
+
+		it('cancels a batch upload when the signal is already aborted', async () => {
+			const uploader = new Uploader()
+			const controller = new AbortController()
+			controller.abort()
+
+			const uploads = await uploader.batchUpload('/dir', [new File(['a'], 'a.txt')], { signal: controller.signal })
+			expect((uploads.at(-1) as unknown as { cancelled: boolean }).cancelled).toBe(true)
+		})
+	})
+
 	describe('upload target resolution', () => {
 		// destination folder source is mocked to https://localhost/remote.php/dav/files/test
 		const defaultRoot = 'https://localhost/remote.php/dav/files/test'
diff --git a/lib/upload/uploader/Uploader.ts b/lib/upload/uploader/Uploader.ts
index d7db7427..5b3e8ff9 100644
--- a/lib/upload/uploader/Uploader.ts
+++ b/lib/upload/uploader/Uploader.ts
@@ -326,7 +326,7 @@ export class Uploader extends TypedEventTarget<UploaderEventsMap> {
 			{ ...options, callback, headers },
 		)
 		if (options?.signal) {
-			options.signal.addEventListener('abort', upload.cancel)
+			this.#attachAbortSignal(options.signal, upload)
 		}
 
 		const uploads = [...upload.initialize(), upload]
@@ -352,7 +352,7 @@ export class Uploader extends TypedEventTarget<UploaderEventsMap> {
 		const headers = Object.fromEntries(this.#customHeaders.entries())
 		const upload = new UploadFile(target, fileHandle, { ...options, headers })
 		if (options?.signal) {
-			options.signal.addEventListener('abort', upload.cancel)
+			this.#attachAbortSignal(options.signal, upload)
 		}
 
 		this.#attachEventListeners(upload)
@@ -363,6 +363,20 @@ export class Uploader extends TypedEventTarget<UploaderEventsMap> {
 		return upload
 	}
 
+	/**
+	 * Cancel the upload when the caller provided abort signal is aborted.
+	 *
+	 * @param signal - The abort signal provided by the caller
+	 * @param upload - The upload to cancel when the signal is aborted
+	 */
+	#attachAbortSignal(signal: AbortSignal, upload: IUpload): void {
+		if (signal.aborted) {
+			upload.cancel()
+			return
+		}
+		signal.addEventListener('abort', () => upload.cancel(), { once: true })
+	}
+
 	/**
 	 * Resolve the absolute upload target for a destination relative to the root folder.
 	 *