diff --git a/app/UI.hs b/app/UI.hs
index 8dc2af1..7d5f114 100644
--- a/app/UI.hs
+++ b/app/UI.hs
@@ -32,6 +32,7 @@ updateUI window webView view = do
 handleAction :: TVar AppState -> Gtk.ApplicationWindow -> WebKit.WebView -> UserAction -> IO ()
 handleAction stateTVar window webView action = do
   st <- atomically $ readTVar stateTVar
+  let totalChapters = length (cAllChapters st)
   case action of
     ZoomIn -> updateZoom stateTVar webView (zoomlvl st + 0.1)
     ZoomOut -> updateZoom stateTVar webView (max 0.1 (zoomlvl st - 0.1))
@@ -42,7 +43,9 @@ handleAction stateTVar window webView action = do
             LoadSpecific i -> i
             _ -> cIdx st
 
-      case prepareView st nextIdx of
+      let safeIdx = max 0 (min (totalChapters -1 ) nextIdx)
+
+      case prepareView st safeIdx of
         Nothing -> pure ()
         Just view -> do
           updateUI window webView view