diff --git a/frontend/src/app/main/errors.cljs b/frontend/src/app/main/errors.cljs
index 0ea0455c5..316a9e16c 100644
--- a/frontend/src/app/main/errors.cljs
+++ b/frontend/src/app/main/errors.cljs
@@ -142,17 +142,23 @@
     (when expl (js/console.error expl))
     (js/console.groupEnd msg)))
 
+(defn on-unhandled-error
+  [error]
+  (if (instance? ExceptionInfo error)
+    (-> error sentry/capture-exception ex-data ptk/handle-error)
+    (let [hint (ex-message error)
+          msg  (str "Unhandled Internal Error: " hint)]
+      (sentry/capture-exception error)
+      (ts/schedule (st/emitf (rt/assign-exception error)))
+      (js/console.group msg)
+      (ex/ignoring (js/console.error error))
+      (js/console.groupEnd msg))))
+
 (defonce uncaught-error-handler
   (letfn [(on-error [event]
             (.preventDefault ^js event)
-            (when-let [error (unchecked-get event "error")]
-              (let [hint (ex-message error)
-                    msg  (str "Unhandled Internal Error: " hint)]
-                (sentry/capture-exception error)
-                (ts/schedule (st/emitf (rt/assign-exception error)))
-                (js/console.group msg)
-                (ex/ignoring (js/console.error error))
-                (js/console.groupEnd msg))))]
+            (some-> (unchecked-get event "error")
+                    (on-unhandled-error)))]
     (.addEventListener js/window "error" on-error)
     (fn []
       (.removeEventListener js/window "error" on-error))))
diff --git a/frontend/src/app/main/ui/viewer.cljs b/frontend/src/app/main/ui/viewer.cljs
index a9eccfee9..148064cdf 100644
--- a/frontend/src/app/main/ui/viewer.cljs
+++ b/frontend/src/app/main/ui/viewer.cljs
@@ -6,6 +6,7 @@
 
 (ns app.main.ui.viewer
   (:require
+   [app.common.exceptions :as ex]
    [app.common.geom.point :as gpt]
    [app.main.data.comments :as dcm]
    [app.main.data.viewer :as dv]
@@ -38,14 +39,10 @@
   [{:keys [params data]}]
 
   (let [{:keys [page-id section index]} params
+        {:keys [file users project perms]} data
 
         local   (mf/deref refs/viewer-local)
 
-        file    (:file data)
-        users   (:users data)
-        project (:project data)
-        perms   (:permissions data)
-
         page-id (or page-id (-> file :data :pages first))
 
         page    (mf/use-memo
@@ -78,6 +75,9 @@
 
     (hooks/use-shortcuts ::viewer sc/shortcuts)
 
+    (when (nil? page)
+      (ex/raise :type :not-found))
+
     ;; Set the page title
     (mf/use-effect
      (mf/deps (:name file))