diff --git a/controllers/Download.php b/controllers/Download.php
index 94e10a5..b5de549 100644
--- a/controllers/Download.php
+++ b/controllers/Download.php
@@ -22,7 +22,7 @@ class Download
 		$album = Tag::fromId($tag);
 
 		if (isset($_SESSION['current_export']))
-			throw new UserFacingException('An export of "' . $tag->tag . '" is ongoing. Please try again later.');
+			throw new UserFacingException('You can only export one album at the same time. Please wait until the other download finishes, or try again later.');
 
 		// So far so good?
 		$this->exportAlbum($album);
@@ -46,6 +46,15 @@ class Download
 			1 => ['pipe', 'w'], // STDOUT
 		];
 
+		// Prevent simultaneous exports.
+		$_SESSION['current_export'] = $album->id_tag;
+
+		// Allow new exports if the connection is terminated unexpectedly (e.g. when a user aborts a download).
+		register_shutdown_function(function() {
+			if (isset($_SESSION['current_export']))
+				unset($_SESSION['current_export']);
+		});
+
 		$command = 'tar -cf - -C ' . escapeshellarg(ASSETSDIR) . ' --null -T -';
 
 		$proc = proc_open($command, $descriptorspec, $pipes, ASSETSDIR);
@@ -92,6 +101,9 @@ class Download
 		fclose($pipes[1]);
 
 		proc_close($proc);
+
+		// Allow new exports from this point onward.
+		unset($_SESSION['current_export']);
 	}
 
 	private function getChildAlbumIds($parent_id)