diff --git a/YKanBan.Tests/TestUtilities/ScriptedDialogService.cs b/YKanBan.Tests/TestUtilities/ScriptedDialogService.cs
index 8562ca2..3956b06 100644
--- a/YKanBan.Tests/TestUtilities/ScriptedDialogService.cs
+++ b/YKanBan.Tests/TestUtilities/ScriptedDialogService.cs
@@ -27,10 +27,12 @@ internal sealed class ScriptedDialogService : IDialogService
         return result ?? false;
     }
 
-    public Task<string?> PickSaveFilePathAsync(string suggestedFileName)
+    public Task<Func<Task<Stream>>?> PickSaveFileAsync(string suggestedFileName)
     {
         SuggestedFileNames.Add(suggestedFileName);
-        return Task.FromResult(SaveFilePath);
+        string? path = SaveFilePath;
+        return Task.FromResult<Func<Task<Stream>>?>(
+            path is null ? null : () => Task.FromResult<Stream>(File.Create(path)));
     }
 
     /// <summary>Answers every confirmation dialog with the given choice.</summary>
diff --git a/YKanBan.Tests/ViewModels/TagsAndSearchViewModelTests.cs b/YKanBan.Tests/ViewModels/TagsAndSearchViewModelTests.cs
index ca638bb..dbebe41 100644
--- a/YKanBan.Tests/ViewModels/TagsAndSearchViewModelTests.cs
+++ b/YKanBan.Tests/ViewModels/TagsAndSearchViewModelTests.cs
@@ -414,5 +414,22 @@ public class TagsAndSearchViewModelTests
         Assert.IsTrue(message.HasDetails);
     }
 
+    [TestMethod]
+    public async Task ExportReadFailureIsReportedAndLeavesTheTargetUntouched()
+    {
+        using var fixture = new Fixture();
+        WorkspaceViewModel workspace = fixture.CreateWorkspace();
+        string path = Path.Combine(fixture.Directory.FullPath, "out.md");
+        File.WriteAllText(path, "previous");
+        fixture.Dialogs.SaveFilePath = path;
+
+        fixture.Repository.Dispose();
+        await workspace.ExportCommand.ExecuteAsync(null);
+
+        var message = (MessageDialogViewModel)fixture.Dialogs.Shown.Single();
+        Assert.AreEqual(Resources.Export_Failed_Title, message.Title);
+        Assert.AreEqual("previous", File.ReadAllText(path));
+    }
+
     #endregion
 }
diff --git a/YKanBan/ViewModels/Dialogs/IDialogService.cs b/YKanBan/ViewModels/Dialogs/IDialogService.cs
index 0be1ec6..8e1a156 100644
--- a/YKanBan/ViewModels/Dialogs/IDialogService.cs
+++ b/YKanBan/ViewModels/Dialogs/IDialogService.cs
@@ -20,8 +20,12 @@ public interface IDialogService
     /// Shows the system save-file dialog for a Markdown file.
     /// </summary>
     /// <param name="suggestedFileName">The proposed file name.</param>
-    /// <returns>The chosen local path, or <see langword="null"/> when the user cancelled.</returns>
-    Task<string?> PickSaveFilePathAsync(string suggestedFileName);
+    /// <returns>
+    /// A function opening the chosen file for writing, emptied first, or
+    /// <see langword="null"/> when the user cancelled. Nothing is created or
+    /// truncated until the function is called.
+    /// </returns>
+    Task<Func<Task<Stream>>?> PickSaveFileAsync(string suggestedFileName);
 }
 
 /// <summary>
diff --git a/YKanBan/ViewModels/WorkspaceViewModel.cs b/YKanBan/ViewModels/WorkspaceViewModel.cs
index 8343658..3a594bf 100644
--- a/YKanBan/ViewModels/WorkspaceViewModel.cs
+++ b/YKanBan/ViewModels/WorkspaceViewModel.cs
@@ -96,18 +96,22 @@ public sealed partial class WorkspaceViewModel : ViewModelBase
     private async Task ExportAsync()
     {
         DateTimeOffset exportedAt = DateTimeOffset.Now;
-        string? path = await _dialogs.PickSaveFilePathAsync(MarkdownExporter.BuildFileName(WorkspaceName, exportedAt));
-        if (path is null)
-        {
-            return;
-        }
-
         try
         {
+            Func<Task<Stream>>? openTarget =
+                await _dialogs.PickSaveFileAsync(MarkdownExporter.BuildFileName(WorkspaceName, exportedAt));
+            if (openTarget is null)
+            {
+                return;
+            }
+
+            // Read everything before opening the target, so a failed read leaves an existing file untouched.
             WorkspaceRepository repository = Session.Repository;
             string markdown = MarkdownExporter.Export(
                 WorkspaceName, repository.GetColumns(), repository.GetCards(), repository.GetTagsWithUsage(), exportedAt);
-            await File.WriteAllTextAsync(path, markdown, new UTF8Encoding(encoderShouldEmitUTF8Identifier: false));
+            await using Stream stream = await openTarget();
+            await using var writer = new StreamWriter(stream, new UTF8Encoding(encoderShouldEmitUTF8Identifier: false));
+            await writer.WriteAsync(markdown);
         }
         catch (Exception exception)
         {
diff --git a/YKanBan/Views/DialogService.cs b/YKanBan/Views/DialogService.cs
index ec54cba..e88d5cb 100644
--- a/YKanBan/Views/DialogService.cs
+++ b/YKanBan/Views/DialogService.cs
@@ -52,7 +52,7 @@ public sealed class DialogService : IDialogService
     }
 
     /// <inheritdoc/>
-    public async Task<string?> PickSaveFilePathAsync(string suggestedFileName)
+    public async Task<Func<Task<Stream>>?> PickSaveFileAsync(string suggestedFileName)
     {
         if (!_owners.TryPeek(out Window? owner))
         {
@@ -69,7 +69,28 @@ public sealed class DialogService : IDialogService
                 new FilePickerFileType(YKanBan.Resources.Export_FileTypeMarkdown) { Patterns = ["*.md"] },
             ],
         });
-        return file?.TryGetLocalPath();
+        if (file is null)
+        {
+            return null;
+        }
+
+        // A local file is replaced through the file system; a target without a
+        // local path (a sandboxed or virtual location) is written through the
+        // storage provider, emptied first because it may already have content.
+        string? localPath = file.TryGetLocalPath();
+        if (localPath is not null)
+        {
+            return () => Task.FromResult<Stream>(new FileStream(localPath, FileMode.Create, FileAccess.Write));
+        }
+        return async () =>
+        {
+            Stream stream = await file.OpenWriteAsync();
+            if (stream.CanSeek)
+            {
+                stream.SetLength(0);
+            }
+            return stream;
+        };
     }
 
     /// <summary>