diff --git a/src/context.ts b/src/context.ts
index d55ccfb..5d13d5d 100644
--- a/src/context.ts
+++ b/src/context.ts
@@ -134,7 +134,10 @@ export class Context {
 					await writer.write(chunk)
 				} catch (err) {
 					await fsPromises.unlink(tempPath).catch(noop)
-					throw err
+					throw new errors.MAP_WRITE_ERROR({
+						message: err instanceof Error ? err.message : undefined,
+						cause: err,
+					})
 				}
 			},
 			close: async () => {
@@ -143,7 +146,10 @@ export class Context {
 					await writer.close()
 				} catch (err) {
 					await fsPromises.unlink(tempPath).catch(noop)
-					throw err
+					throw new errors.MAP_WRITE_ERROR({
+						message: err instanceof Error ? err.message : undefined,
+						cause: err,
+					})
 				}
 
 				// Validate the uploaded map file BEFORE replacing the existing one
diff --git a/src/lib/errors.ts b/src/lib/errors.ts
index ffbd7e1..a231558 100644
--- a/src/lib/errors.ts
+++ b/src/lib/errors.ts
@@ -98,6 +98,11 @@ const errorsList = [
 		message: 'Invalid map file',
 		status: 400,
 	},
+	{
+		code: 'MAP_WRITE_ERROR',
+		message: 'Failed to write map data',
+		status: 500,
+	},
 
 	// Generic errors
 	{
diff --git a/test/map-shares.test.ts b/test/map-shares.test.ts
index e218e81..8e49745 100644
--- a/test/map-shares.test.ts
+++ b/test/map-shares.test.ts
@@ -12,7 +12,7 @@ import {
 	fetch as secretStreamFetch,
 	Agent as SecretStreamAgent,
 } from 'secret-stream-http'
-import { describe, it, expect } from 'vitest'
+import { describe, it, expect, vi } from 'vitest'
 
 import type { MapShareState } from '../src/types.js'
 import {
@@ -150,7 +150,9 @@ describe('Map Shares and Downloads', () => {
 
 			// Create a third device (another receiver)
 			const receiver2KeyPair = SecretStreamAgent.keyPair(Buffer.alloc(32, 2))
-			const receiver2DeviceId = Buffer.from(receiver2KeyPair.publicKey).toString('hex')
+			const receiver2DeviceId = Buffer.from(
+				receiver2KeyPair.publicKey,
+			).toString('hex')
 
 			// Create share for first receiver
 			const share1 = await createShare().json()
@@ -1104,7 +1106,9 @@ describe('Map Shares and Downloads', () => {
 
 				// Create a third device with different keys
 				const wrongKeyPair = SecretStreamAgent.keyPair()
-				const wrongDeviceId = Buffer.from(wrongKeyPair.publicKey).toString('hex')
+				const wrongDeviceId = Buffer.from(wrongKeyPair.publicKey).toString(
+					'hex',
+				)
 
 				// Create a share for a different device
 				const { shareId: shareId2 } = await sender
@@ -1134,7 +1138,9 @@ describe('Map Shares and Downloads', () => {
 
 				// Create a third device with different keys
 				const wrongKeyPair = SecretStreamAgent.keyPair()
-				const wrongDeviceId = Buffer.from(wrongKeyPair.publicKey).toString('hex')
+				const wrongDeviceId = Buffer.from(wrongKeyPair.publicKey).toString(
+					'hex',
+				)
 
 				// Create a share for wrongDeviceId
 				const { shareId } = await sender
@@ -1187,7 +1193,9 @@ describe('Map Shares and Downloads', () => {
 
 				// Create a third device
 				const wrongKeyPair = SecretStreamAgent.keyPair()
-				const wrongDeviceId = Buffer.from(wrongKeyPair.publicKey).toString('hex')
+				const wrongDeviceId = Buffer.from(wrongKeyPair.publicKey).toString(
+					'hex',
+				)
 
 				// Create a share for wrongDeviceId
 				const { shareId } = await sender
@@ -1638,6 +1646,51 @@ describe('Map Shares and Downloads', () => {
 			expect(tempFiles).toHaveLength(0)
 		})
 
+		it('should report MAP_WRITE_ERROR when write fails during download', async (t) => {
+			const { createShare, createDownload, receiver } = await startServers(t)
+			const receiverDir = path.dirname(receiver.customMapPath)
+			const receiverBasename = path.basename(receiver.customMapPath)
+
+			// Mock fs.createWriteStream on the receiver to simulate disk-full
+			const originalCreateWriteStream = fs.createWriteStream
+			const spy = vi
+				.spyOn(fs, 'createWriteStream')
+				.mockImplementation((...args: any[]) => {
+					const stream = originalCreateWriteStream.apply(fs, args as any)
+					stream._write = (
+						_chunk: any,
+						_encoding: BufferEncoding,
+						callback: (error?: Error | null) => void,
+					) => {
+						callback(new Error('ENOSPC: no space left on device'))
+					}
+					return stream
+				})
+			t.onTestFinished(() => spy.mockRestore())
+
+			const share = await createShare().json()
+			const download = await createDownload(share).json<any>()
+
+			// Wait for download to fail
+			await eventsUntil(receiver, download.downloadId, 'error')
+
+			// Check download state has MAP_WRITE_ERROR
+			const downloadStatus = await receiver
+				.get(`downloads/${download.downloadId}`)
+				.json<any>()
+			expect(downloadStatus.status).toBe('error')
+			expect(downloadStatus).toHaveProperty('error.code', 'MAP_WRITE_ERROR')
+
+			await delay(100)
+
+			// Verify temp files are cleaned up
+			const files = fs.readdirSync(receiverDir)
+			const tempFiles = files.filter(
+				(f) => f.startsWith(receiverBasename) && f.includes('.download-'),
+			)
+			expect(tempFiles).toHaveLength(0)
+		})
+
 		it('should try next URL when first mapShareUrl fails during download', async (t) => {
 			const { createShare, sender, receiver } = await startServers(t)
 
diff --git a/test/maps.test.ts b/test/maps.test.ts
index 11c2d3c..9e77397 100644
--- a/test/maps.test.ts
+++ b/test/maps.test.ts
@@ -603,6 +603,8 @@ describe('Map Upload', () => {
 		})
 
 		expect(response.status).toBe(500)
+		const error = await response.json()
+		expect(error).toHaveProperty('code', 'MAP_WRITE_ERROR')
 
 		// Allow time for async cleanup to complete
 		await delay(100)
@@ -646,6 +648,8 @@ describe('Map Upload', () => {
 		})
 
 		expect(response.status).toBe(500)
+		const error = await response.json()
+		expect(error).toHaveProperty('code', 'MAP_WRITE_ERROR')
 
 		// Allow time for async cleanup to complete
 		await delay(100)