diff --git a/frontend/src/app/main/data/viewer.cljs b/frontend/src/app/main/data/viewer.cljs
index fc03e684b8..c2d42d680c 100644
--- a/frontend/src/app/main/data/viewer.cljs
+++ b/frontend/src/app/main/data/viewer.cljs
@@ -304,6 +304,7 @@
             index   (some-> (:index params) parse-long)
 
             frames  (dm/get-in state [:viewer :pages page-id :frames])
+            index   (min (or index 0) (max 0 (dec (count frames))))
             srect   (-> (nth frames index)
                         (get :selrect))
             osize   (dm/get-in state [:viewer-local :viewport-size])
@@ -327,6 +328,7 @@
             index   (some-> (:index params) parse-long)
 
             frames  (dm/get-in state [:viewer :pages page-id :frames])
+            index   (min (or index 0) (max 0 (dec (count frames))))
             srect   (-> (nth frames index)
                         (get :selrect))
 
diff --git a/frontend/test/frontend_tests/data/viewer_test.cljs b/frontend/test/frontend_tests/data/viewer_test.cljs
new file mode 100644
index 0000000000..1af06766f2
--- /dev/null
+++ b/frontend/test/frontend_tests/data/viewer_test.cljs
@@ -0,0 +1,69 @@
+;; This Source Code Form is subject to the terms of the Mozilla Public
+;; License, v. 2.0. If a copy of the MPL was not distributed with this
+;; file, You can obtain one at http://mozilla.org/MPL/2.0/.
+;;
+;; Copyright (c) KALEIDOS INC
+
+(ns frontend-tests.data.viewer-test
+  (:require
+   [app.common.uuid :as uuid]
+   [app.main.data.viewer :as dv]
+   [cljs.test :as t]
+   [potok.v2.core :as ptk]))
+
+(def ^:private page-id
+  (uuid/custom 1 1))
+
+(defn- base-state
+  "Build a minimal viewer state with the given frames and query-params."
+  [{:keys [frames index]}]
+  {:route {:params {:query {:page-id (str page-id)
+                            :index   (str index)}}}
+   :viewer {:pages {page-id {:frames frames}}}
+   :viewer-local {:viewport-size {:width 1000 :height 800}}})
+
+(t/deftest zoom-to-fit-clamps-out-of-bounds-index
+  (t/testing "index exceeds frame count"
+    (let [state (base-state {:frames [{:selrect {:width 100 :height 100}}]
+                             :index  1})
+          result (ptk/update dv/zoom-to-fit state)]
+      (t/is (= (get-in result [:viewer-local :zoom-type]) :fit))
+      (t/is (number? (get-in result [:viewer-local :zoom])))))
+
+  (t/testing "index is zero with single frame (normal case)"
+    (let [state (base-state {:frames [{:selrect {:width 100 :height 100}}]
+                             :index  0})
+          result (ptk/update dv/zoom-to-fit state)]
+      (t/is (= (get-in result [:viewer-local :zoom-type]) :fit))
+      (t/is (number? (get-in result [:viewer-local :zoom])))))
+
+  (t/testing "index within valid range with multiple frames"
+    (let [state (base-state {:frames [{:selrect {:width 100 :height 100}}
+                                      {:selrect {:width 200 :height 200}}]
+                             :index  1})
+          result (ptk/update dv/zoom-to-fit state)]
+      (t/is (= (get-in result [:viewer-local :zoom-type]) :fit))
+      (t/is (number? (get-in result [:viewer-local :zoom]))))))
+
+(t/deftest zoom-to-fill-clamps-out-of-bounds-index
+  (t/testing "index exceeds frame count"
+    (let [state (base-state {:frames [{:selrect {:width 100 :height 100}}]
+                             :index  1})
+          result (ptk/update dv/zoom-to-fill state)]
+      (t/is (= (get-in result [:viewer-local :zoom-type]) :fill))
+      (t/is (number? (get-in result [:viewer-local :zoom])))))
+
+  (t/testing "index is zero with single frame (normal case)"
+    (let [state (base-state {:frames [{:selrect {:width 100 :height 100}}]
+                             :index  0})
+          result (ptk/update dv/zoom-to-fill state)]
+      (t/is (= (get-in result [:viewer-local :zoom-type]) :fill))
+      (t/is (number? (get-in result [:viewer-local :zoom])))))
+
+  (t/testing "index within valid range with multiple frames"
+    (let [state (base-state {:frames [{:selrect {:width 100 :height 100}}
+                                      {:selrect {:width 200 :height 200}}]
+                             :index  1})
+          result (ptk/update dv/zoom-to-fill state)]
+      (t/is (= (get-in result [:viewer-local :zoom-type]) :fill))
+      (t/is (number? (get-in result [:viewer-local :zoom]))))))
diff --git a/frontend/test/frontend_tests/runner.cljs b/frontend/test/frontend_tests/runner.cljs
index 1d189cbafe..fe709f8a2f 100644
--- a/frontend/test/frontend_tests/runner.cljs
+++ b/frontend/test/frontend_tests/runner.cljs
@@ -3,6 +3,7 @@
    [cljs.test :as t]
    [frontend-tests.basic-shapes-test]
    [frontend-tests.data.repo-test]
+   [frontend-tests.data.viewer-test]
    [frontend-tests.data.workspace-colors-test]
    [frontend-tests.data.workspace-texts-test]
    [frontend-tests.helpers-shapes-test]
@@ -39,6 +40,7 @@
   (t/run-tests
    'frontend-tests.basic-shapes-test
    'frontend-tests.data.repo-test
+   'frontend-tests.data.viewer-test
    'frontend-tests.data.workspace-colors-test
    'frontend-tests.data.workspace-texts-test
    'frontend-tests.helpers-shapes-test
@@ -56,9 +58,9 @@
    'frontend-tests.tokens.logic.token-remapping-test
    'frontend-tests.tokens.style-dictionary-test
    'frontend-tests.tokens.token-errors-test
+   'frontend-tests.tokens.workspace-tokens-remap-test
    'frontend-tests.ui.ds-controls-numeric-input-test
    'frontend-tests.util-object-test
    'frontend-tests.util-range-tree-test
    'frontend-tests.util-simple-math-test
-   'frontend-tests.tokens.workspace-tokens-remap-test
    'frontend-tests.worker-snap-test))