diff --git a/renderer/index.js b/renderer/index.js
index 24b9145d..bd127e7d 100644
--- a/renderer/index.js
+++ b/renderer/index.js
@@ -717,7 +717,7 @@ function torrentError (torrentKey, message) {
 
   // TODO: WebTorrent should have semantic errors
   if (message.startsWith('There is already a swarm')) {
-    onError(new Error('Couldn\'t add duplicate torrent'))
+    onError(new Error('Can\'t add duplicate torrent'))
   } else if (!torrentSummary) {
     onError(message)
   } else {
diff --git a/renderer/webtorrent.js b/renderer/webtorrent.js
index e5a9cf4a..48a769bb 100644
--- a/renderer/webtorrent.js
+++ b/renderer/webtorrent.js
@@ -77,6 +77,12 @@ function startTorrenting (torrentKey, torrentID, path, fileModtimes) {
   } catch (err) {
     return ipc.send('wt-error', torrentKey, err.message)
   }
+  // If we add a duplicate magnet URI or infohash, WebTorrent returns the
+  // existing torrent object! (If we add a duplicate torrent file, it creates a
+  // new torrent object and raises an error later.) Workaround:
+  if (torrent.key) {
+    return ipc.send('wt-error', torrentKey, 'Can\'t add duplicate torrent')
+  }
   torrent.key = torrentKey
   addTorrentEvents(torrent)
   return torrent