diff --git a/lib/Job/BackupRun.php b/lib/Job/BackupRun.php
index ca928b5..86ef1e5 100644
--- a/lib/Job/BackupRun.php
+++ b/lib/Job/BackupRun.php
@@ -133,7 +133,7 @@ final class BackupRun {
 
 		if ($state['phase'] === 'finish') {
 			$segments = $state['segments'];
-			$repo->writeSnapshot($state['snapshot'],
+			$repo->putSnapshot($state['snapshot'],
 				['time' => $state['started'], 'parent' => $state['parent'], 'label' => $state['label'],
 					'roots' => array_keys($state['roots']), 'stats' => $state['stats']] + $state['meta'],
 				(function () use ($repo, $segments) {
@@ -141,7 +141,7 @@ final class BackupRun {
 						yield from $repo->readLines($blobs);
 					}
 				})());
-			$state['phase'] = 'done';
+			$state['phase'] = 'commit';
 		}
 		return $state;
 	}
diff --git a/lib/Repository/Repository.php b/lib/Repository/Repository.php
index 51e0999..5e51c51 100644
--- a/lib/Repository/Repository.php
+++ b/lib/Repository/Repository.php
@@ -288,6 +288,17 @@ final class Repository {
 	 * @param iterable<string> $lines
 	 */
 	public function writeSnapshot(string $snapshotId, array $meta, iterable $lines): void {
+		$this->putSnapshot($snapshotId, $meta, $lines);
+		$this->recordSnapshot($snapshotId);
+	}
+
+	/**
+	 * Store a snapshot object without touching the catalog. Use recordSnapshot() afterwards, from a
+	 * repository opened inside the catalog lock, so the catalog write builds on the latest generation.
+	 *
+	 * @param iterable<string> $lines
+	 */
+	public function putSnapshot(string $snapshotId, array $meta, iterable $lines): void {
 		$tree = fopen('php://temp/maxmemory:' . (4 * 1048576), 'w+b');
 		fwrite($tree, json_encode(['snapshot' => $snapshotId] + $meta, JSON_THROW_ON_ERROR) . "\n");
 		foreach ($lines as $line) {
@@ -301,6 +312,9 @@ final class Repository {
 		fclose($tree);
 		rewind($encrypted);
 		$this->backend->put('snapshots/' . $snapshotId, $encrypted);
+	}
+
+	public function recordSnapshot(string $snapshotId): void {
 		$this->catalog->snapshots[$snapshotId] = true;
 		$this->catalog->write();
 	}
diff --git a/lib/Service/BackupService.php b/lib/Service/BackupService.php
index 3d2ae34..3649383 100644
--- a/lib/Service/BackupService.php
+++ b/lib/Service/BackupService.php
@@ -147,6 +147,17 @@ final class BackupService {
 				}
 			} else {
 				$state['files'] = BackupRun::step($repo, $state['files'], $deadline);
+				if ($state['files']['phase'] === 'commit') {
+					// Catalog write under the catalog lock, from a repository opened inside it: a per-user
+					// export or restore may have written the catalog since this step opened $repo.
+					try {
+						$this->leases->with(PruneService::catalogLockKey($target), LeaseService::EXCLUSIVE, 30,
+							fn () => $this->targets->repository($target)->recordSnapshot((string)$state['files']['snapshot']));
+						$state['files']['phase'] = 'done';
+					} catch (LockedException) {
+						// Another catalog write is in progress: the next step retries this commit.
+					}
+				}
 				if ($state['files']['phase'] === 'done') {
 					$this->recordSnapshot($run, $state['files']);
 					$this->alerts->storedBytes($target, $repo->storedBytes());
diff --git a/tests/Unit/Job/BackupRunTest.php b/tests/Unit/Job/BackupRunTest.php
index 9df3667..6ad73c4 100644
--- a/tests/Unit/Job/BackupRunTest.php
+++ b/tests/Unit/Job/BackupRunTest.php
@@ -27,13 +27,14 @@ class BackupRunTest extends TestCase {
 
 		$state = BackupRun::start($src);
 		$steps = 0;
-		while ($state['phase'] !== 'done' && $steps < 500) {
+		while ($state['phase'] !== 'commit' && $steps < 500) {
 			// Fresh repository object per step, state through JSON: as separate processes would.
 			$repo = Repository::openWithKey($backend, $keys);
 			$state = json_decode(json_encode(BackupRun::step($repo, $state, microtime(true) + 0.05)), true);
 			$steps++;
 		}
-		$this->assertSame('done', $state['phase']);
+		$this->assertSame('commit', $state['phase']);
+		Repository::openWithKey($backend, $keys)->recordSnapshot($state['snapshot']);
 		$this->assertGreaterThan(2, $steps, 'the run was actually split into steps');
 
 		$target = $this->tempDir();
@@ -50,7 +51,7 @@ class BackupRunTest extends TestCase {
 
 		$state = BackupRun::start($src);
 		$mutated = false;
-		for ($i = 0; $i < 500 && $state['phase'] !== 'done'; $i++) {
+		for ($i = 0; $i < 500 && $state['phase'] !== 'commit'; $i++) {
 			$state = BackupRun::step(Repository::openWithKey($backend, $keys), $state, microtime(true) + 0.01);
 			if (!$mutated && $state['cur'] !== null && $state['cur']['offset'] > 0) {
 				$fh = fopen("$src/big.bin", 'r+b');
@@ -60,6 +61,8 @@ class BackupRunTest extends TestCase {
 				$mutated = true;
 			}
 		}
+		$this->assertSame('commit', $state['phase']);
+		Repository::openWithKey($backend, $keys)->recordSnapshot($state['snapshot']);
 		$this->assertTrue($mutated);
 		$this->assertGreaterThanOrEqual(1, $state['stats']['retried'] ?? 0);
 		$target = $this->tempDir();
@@ -78,14 +81,17 @@ class BackupRunTest extends TestCase {
 		Repository::initWithKey($backend, $keys, $keys->wrap('pw'));
 		$run = function (?string $parent) use ($backend, $src, $keys): array {
 			$state = BackupRun::start(['data' => $src], $parent);
-			for ($i = 0; $i < 2000 && $state['phase'] !== 'done'; $i++) {
+			for ($i = 0; $i < 2000 && $state['phase'] !== 'commit'; $i++) {
 				$state = json_decode(json_encode(BackupRun::step(Repository::openWithKey($backend, $keys), $state, microtime(true))), true);
 			}
+			if ($state['phase'] === 'commit') {
+				Repository::openWithKey($backend, $keys)->recordSnapshot($state['snapshot']);
+			}
 			return $state;
 		};
 		$first = $run(null);
 		$second = $run($first['snapshot']);
-		$this->assertSame('done', $second['phase']);
+		$this->assertSame('commit', $second['phase']);
 		$this->assertGreaterThan(150, $second["steps"], "one file per step");
 		$this->assertSame(0, $second['stats']['read'], 'merge-join with the parent across steps reuses every file');
 		$this->assertSame(200, $second['stats']['reused']);