diff --git a/lib/Service/DocumentService.php b/lib/Service/DocumentService.php
index d4bcdf01747..0f8ca17cf02 100644
--- a/lib/Service/DocumentService.php
+++ b/lib/Service/DocumentService.php
@@ -307,6 +307,7 @@ public function getSteps(int $documentId, int $lastVersion): array {
 
 	/**
 	 * @throws DocumentSaveConflictException
+	 * @throws DoesNotExistException
 	 * @throws InvalidPathException
 	 * @throws NotFoundException
 	 */
@@ -331,7 +332,16 @@ public function assertNoOutsideConflict(Document $document, File $file, bool $fo
 		$fileChecksum = self::computeCheckSum($fileContent);
 
 		if ($storedChecksum !== $fileChecksum) {
-			throw new DocumentSaveConflictException('File changed in the meantime from outside');
+			// $document was loaded at the start of the request.
+			// A save request handled in the meantime is not reflected in it
+			// and would be mistaken for an outside change.
+			// Reload the document to compare against the latest saved state.
+			$document = $this->documentMapper->find($documentId);
+			if ($document->getChecksum() !== $fileChecksum) {
+				throw new DocumentSaveConflictException('File changed in the meantime from outside');
+			}
+			// The save request already stored the latest version info.
+			return;
 		}
 
 		$document->setLastSavedVersionTime($fileMtime);
diff --git a/tests/unit/Service/DocumentServiceTest.php b/tests/unit/Service/DocumentServiceTest.php
new file mode 100644
index 00000000000..bf22c06aa68
--- /dev/null
+++ b/tests/unit/Service/DocumentServiceTest.php
@@ -0,0 +1,150 @@
+<?php
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Text\Tests;
+
+use OCA\Text\Db\Document;
+use OCA\Text\Db\DocumentMapper;
+use OCA\Text\Db\SessionMapper;
+use OCA\Text\Db\StepMapper;
+use OCA\Text\Exception\DocumentSaveConflictException;
+use OCA\Text\Service\DocumentService;
+use OCA\Text\Service\FileService;
+use OCA\Text\Service\LockService;
+use OCP\DirectEditing\IManager;
+use OCP\Files\Config\IUserMountCache;
+use OCP\Files\File;
+use OCP\Files\IAppData;
+use OCP\Files\IRootFolder;
+use OCP\ICache;
+use OCP\ICacheFactory;
+use OCP\IConfig;
+use OCP\IRequest;
+use Psr\Log\LoggerInterface;
+
+class DocumentServiceTest extends \PHPUnit\Framework\TestCase {
+	private DocumentService $documentService;
+
+	private DocumentMapper $documentMapper;
+	private FileService $fileService;
+	private ICache $cache;
+
+	public function setUp(): void {
+		$this->documentMapper = $this->createMock(DocumentMapper::class);
+		$this->fileService = $this->createMock(FileService::class);
+		$this->cache = $this->createMock(ICache::class);
+		$cacheFactory = $this->createMock(ICacheFactory::class);
+		$cacheFactory->method('createDistributed')->willReturn($this->cache);
+		$request = $this->createMock(IRequest::class);
+		$request->method('getParam')->willReturn(null);
+
+		$this->fileService->method('isReadOnly')->willReturn(false);
+
+		$this->documentService = new DocumentService(
+			$this->documentMapper,
+			$this->fileService,
+			$this->createMock(StepMapper::class),
+			$this->createMock(SessionMapper::class),
+			$this->createMock(IAppData::class),
+			'admin',
+			$this->createMock(IRootFolder::class),
+			$cacheFactory,
+			$this->createMock(LoggerInterface::class),
+			$this->createMock(LockService::class),
+			$request,
+			$this->createMock(IManager::class),
+			$this->createMock(IUserMountCache::class),
+			$this->createMock(IConfig::class),
+		);
+	}
+
+	private function createDocument(string $etag, int $mtime, string $content): Document {
+		$document = new Document();
+		$document->setId(123);
+		$document->setLastSavedVersionEtag($etag);
+		$document->setLastSavedVersionTime($mtime);
+		$document->setChecksum(DocumentService::computeCheckSum($content));
+		return $document;
+	}
+
+	private function mockFile(string $etag, int $mtime, string $content): File {
+		$file = $this->createMock(File::class);
+		$file->method('getEtag')->willReturn($etag);
+		$file->method('getMtime')->willReturn($mtime);
+		$file->method('getContent')->willReturn($content);
+		return $file;
+	}
+
+	public function testNoConflictWhenVersionInfoMatches(): void {
+		$document = $this->createDocument('etag1', 1000, 'content');
+		$file = $this->mockFile('etag1', 1000, 'content');
+
+		$this->documentMapper->expects(self::never())->method('find');
+		$this->documentMapper->expects(self::never())->method('update');
+
+		$this->documentService->assertNoOutsideConflict($document, $file);
+	}
+
+	public function testRefreshesVersionInfoWhenContentMatches(): void {
+		$document = $this->createDocument('etag1', 1000, 'content');
+		$file = $this->mockFile('etag2', 2000, 'content');
+
+		$this->documentMapper->expects(self::never())->method('find');
+		$this->documentMapper->expects(self::once())
+			->method('update')
+			->with($document);
+
+		$this->documentService->assertNoOutsideConflict($document, $file);
+		self::assertSame('etag2', $document->getLastSavedVersionEtag());
+		self::assertSame(2000, $document->getLastSavedVersionTime());
+	}
+
+	public function testNoConflictWhenOwnSaveFinishedInTheMeantime(): void {
+		// Loaded at the start of the request - stale by now.
+		$document = $this->createDocument('etag1', 1000, 'old content');
+		// A save request updated the file in the meantime ...
+		$file = $this->mockFile('etag2', 2000, 'new content');
+		// ... and stored the new version info in the document.
+		$freshDocument = $this->createDocument('etag2', 2000, 'new content');
+
+		$this->documentMapper->expects(self::once())
+			->method('find')
+			->with(123)
+			->willReturn($freshDocument);
+		$this->documentMapper->expects(self::never())->method('update');
+
+		$this->documentService->assertNoOutsideConflict($document, $file);
+	}
+
+	public function testConflictWhenFileChangedFromOutside(): void {
+		$document = $this->createDocument('etag1', 1000, 'old content');
+		$file = $this->mockFile('etag2', 2000, 'outside content');
+		// The latest saved state does not match the file either.
+		$freshDocument = $this->createDocument('etag1', 1000, 'old content');
+
+		$this->documentMapper->expects(self::once())
+			->method('find')
+			->with(123)
+			->willReturn($freshDocument);
+
+		$this->expectException(DocumentSaveConflictException::class);
+		$this->documentService->assertNoOutsideConflict($document, $file);
+	}
+
+	public function testNoConflictWhileSaveLockIsHeld(): void {
+		$document = $this->createDocument('etag1', 1000, 'old content');
+		$file = $this->mockFile('etag2', 2000, 'new content');
+
+		$this->cache->method('get')
+			->with('document-save-lock-123')
+			->willReturn(true);
+		$this->documentMapper->expects(self::never())->method('find');
+		$this->documentMapper->expects(self::never())->method('update');
+
+		$this->documentService->assertNoOutsideConflict($document, $file);
+	}
+}