diff --git a/frontend/public/locales/en-GB/translation.json b/frontend/public/locales/en-GB/translation.json
index 98dd7c10e..a35ba10ee 100644
--- a/frontend/public/locales/en-GB/translation.json
+++ b/frontend/public/locales/en-GB/translation.json
@@ -2202,6 +2202,15 @@
       "processing": "Analysing differences...",
       "complete": "Comparison ready"
     },
+    "longJob": {
+      "title": "Large comparison in progress",
+      "body": "These PDFs together exceed 2,000 pages. Processing can take several minutes."
+    },
+    "slowOperation": {
+      "title": "Still working…",
+      "body": "This comparison is taking longer than usual. You can let it continue or cancel it.",
+      "cancel": "Cancel comparison"
+    },
     "pageCount": "{{count}} pages",
     "lastModified": "Last modified",
     "newLine": "new-line",
diff --git a/frontend/public/locales/en-US/translation.json b/frontend/public/locales/en-US/translation.json
index 0f4f42872..93dab8a0f 100644
--- a/frontend/public/locales/en-US/translation.json
+++ b/frontend/public/locales/en-US/translation.json
@@ -1341,6 +1341,15 @@
       "processing": "Analyzing differences...",
       "complete": "Comparison ready"
     },
+    "longJob": {
+      "title": "Large comparison in progress",
+      "body": "These PDFs together exceed 2,000 pages. Processing can take several minutes."
+    },
+    "slowOperation": {
+      "title": "Still working…",
+      "body": "This comparison is taking longer than usual. You can let it continue or cancel it.",
+      "cancel": "Cancel comparison"
+    },
     "error": {
       "selectRequired": "Select a base and comparison document.",
       "filesMissing": "Unable to locate the selected files. Please re-select them.",
diff --git a/frontend/src/components/tools/compare/types.ts b/frontend/src/components/tools/compare/types.ts
index 7b85ebb77..684f13200 100644
--- a/frontend/src/components/tools/compare/types.ts
+++ b/frontend/src/components/tools/compare/types.ts
@@ -5,7 +5,7 @@ export interface PagePreview {
   width: number;
   height: number;
   rotation: number;
-  url: string;
+  url: string | null;
 }
 
 export interface WordHighlightEntry {