diff --git a/packages/web-pkg/src/components/AppTemplates/AppWrapper.vue b/packages/web-pkg/src/components/AppTemplates/AppWrapper.vue
index 92ff71b56d8..2d6f43b4277 100644
--- a/packages/web-pkg/src/components/AppTemplates/AppWrapper.vue
+++ b/packages/web-pkg/src/components/AppTemplates/AppWrapper.vue
@@ -103,6 +103,7 @@ import { DavPermission } from '@opencloud-eu/web-client/webdav'
 import { HttpError } from '@opencloud-eu/web-client'
 import { dirname } from 'path'
 import { useFileActionsOpenWithApp } from '../../composables'
+import { ResourceNotFoundError } from '../../errors'
 import { UnsavedChangesModal } from '../Modals'
 import {
   decodeTextContent,
@@ -175,7 +176,10 @@ const loading = ref(!unref(noResourceLoading))
 const loadingError: Ref<Error> = ref()
 // apps that load their files themselves (e.g. the preview) report errors via the folder loading
 const error = computed(() => unref(loadingError) || unref(folderLoadingError))
-const isNotFoundError = computed(() => (unref(error) as HttpError)?.statusCode === 404)
+const isNotFoundError = computed(() => {
+  const e = unref(error)
+  return e instanceof ResourceNotFoundError || (e as HttpError)?.statusCode === 404
+})
 const isReadOnly = ref(false)
 /** The loaded text is not valid UTF-8, see `getFileContentsAsText`. */
 const isLossyContent = ref(false)
@@ -420,9 +424,16 @@ const addMissingDriveAliasAndItem = async () => {
 const loadResourceTask = useTask(function* (signal) {
   try {
     if (!unref(driveAliasAndItem)) {
+      if (!unref(fileId)) {
+        throw new ResourceNotFoundError('No file given')
+      }
       yield addMissingDriveAliasAndItem()
     }
     space.value = unref(unref(currentFileContext).space)
+    if (!unref(space)) {
+      // the space is unknown or not accessible, like the server answers for such resources
+      throw new ResourceNotFoundError('Space not found')
+    }
     const currentSpace = unref(space)
     if (isPublicSpaceResource(currentSpace) && currentSpace.publicLinkPermission === undefined) {
       // the link permission and file id are only known if the link got resolved beforehand,
diff --git a/packages/web-pkg/src/errors/types.ts b/packages/web-pkg/src/errors/types.ts
index 9e9571a3690..2cd309c0ad9 100644
--- a/packages/web-pkg/src/errors/types.ts
+++ b/packages/web-pkg/src/errors/types.ts
@@ -18,3 +18,10 @@ export class RuntimeError extends Error {
 export class ApiError extends RuntimeError {
   name = 'ApiError'
 }
+
+/**
+ * error for resources that can't be found without the server telling so, e.g. an unknown space
+ */
+export class ResourceNotFoundError extends RuntimeError {
+  name = 'ResourceNotFoundError'
+}
diff --git a/packages/web-pkg/tests/unit/components/AppTemplates/AppWrapper.spec.ts b/packages/web-pkg/tests/unit/components/AppTemplates/AppWrapper.spec.ts
index 43f9d9c7e11..01069f98eb0 100644
--- a/packages/web-pkg/tests/unit/components/AppTemplates/AppWrapper.spec.ts
+++ b/packages/web-pkg/tests/unit/components/AppTemplates/AppWrapper.spec.ts
@@ -18,6 +18,7 @@ import type { YjsSession, YjsStatus } from '../../../../src/composables/yjs'
 import type { FileContentOptions, FileContext } from '../../../../src/composables/appDefaults'
 import type { FileAction } from '../../../../src/composables/actions'
 import { eventBus } from '../../../../src/services'
+import { ResourceNotFoundError } from '../../../../src/errors'
 import {
   type CustomComponentExtension,
   useExtensionRegistry,
@@ -126,6 +127,7 @@ function setup({
     params: { driveAliasAndItem: 'personal/alan/a.md' }
   }),
   isGuestContext = false,
+  fileContext = mock<FileContext>({ space: mock<any>(), path: '/a.md' }),
   fileContentOptions = undefined as FileContentOptions,
   // Receives the errors Vue would otherwise report as unhandled.
   errorHandler = undefined as (err: unknown) => void
@@ -144,7 +146,7 @@ function setup({
     isConflicted.value = true
   })
   const statusRef = ref(status)
-  const currentFileContext = ref(mock<FileContext>({ space: mock<any>(), path: '/a.md' }))
+  const currentFileContext = ref(fileContext)
   // Deferred so the test controls when each half of the load completes.
   let resolveInfo: (r: Resource) => void
   let rejectInfo: (e: Error) => void
@@ -286,6 +288,7 @@ function setup({
     markConflicted,
     putFileContents,
     closeApp,
+    getFileInfo,
     getFileContents,
     unregisterAppBarExtension,
     wasWrittenByRoom,
@@ -436,6 +439,8 @@ describe('AppWrapper — missing drive alias', () => {
     const s = setup({
       yjsEnabled: false,
       currentRoute: route as unknown as RouteLocation,
+      // the drive resolver only finds the space once the route has the drive alias
+      fileContext: { space: undefined, path: '' } as FileContext,
       errorHandler
     })
     // Like the router: the new route changes the file context, which restarts
@@ -456,6 +461,55 @@ describe('AppWrapper — missing drive alias', () => {
   })
 })
 
+describe('AppWrapper — space that cannot be resolved', () => {
+  // e.g. the space of another user, whose alias the drive resolver doesn't know
+  const unresolvedFileContext = { space: undefined, path: '' } as FileContext
+
+  // no mock: it would hand out a file id for any query item
+  function routeWithoutFileId(driveAliasAndItem: string) {
+    return {
+      path: '/test-app',
+      query: {},
+      params: { driveAliasAndItem }
+    } as unknown as RouteLocation
+  }
+
+  function expectNotFoundMessage(s: ReturnType<typeof setup>) {
+    expect(consoleErrorSpy).toHaveBeenCalledWith(expect.any(ResourceNotFoundError))
+    expect(s.wrapper.find('#app-wrapper-not-found-message').exists()).toBe(true)
+    expect(s.wrapper.findComponent({ name: 'ErrorScreen' }).exists()).toBe(false)
+  }
+
+  it('shows the not found message instead of loading the file without a space', async () => {
+    const s = setup({
+      yjsEnabled: false,
+      fileContext: unresolvedFileContext,
+      currentRoute: routeWithoutFileId('project/doesnotexist/x.md')
+    })
+    await flushPromises()
+
+    expect(s.getFileInfo).not.toHaveBeenCalled()
+    expect(getResourceContextSpy).not.toHaveBeenCalled()
+    expectNotFoundMessage(s)
+  })
+
+  it('shows the not found message for the app route without a file', async () => {
+    const errorHandler = vi.fn()
+    const s = setup({
+      yjsEnabled: false,
+      fileContext: unresolvedFileContext,
+      currentRoute: routeWithoutFileId(''),
+      errorHandler
+    })
+    await flushPromises()
+
+    expect(getResourceContextSpy).not.toHaveBeenCalled()
+    expect(s.getFileInfo).not.toHaveBeenCalled()
+    expect(errorHandler).not.toHaveBeenCalled()
+    expectNotFoundMessage(s)
+  })
+})
+
 describe('AppWrapper — closing the app while the file is loading', () => {
   it('stops loading without an error', async () => {
     const errorHandler = vi.fn()