diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
index dbdab05..0aa42c3 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
@@ -16,6 +16,7 @@
  */
 
 import {CommentRange} from '../../../types/common';
+import {FILE, LineNumber} from './gr-diff-line';
 
 export enum DiffSide {
   LEFT = 'left',
@@ -41,3 +42,12 @@
     a.end_character === b.end_character
   );
 }
+
+export function getLineNumber(lineEl?: Element | null): LineNumber | null {
+  if (!lineEl) return null;
+  const lineNumberStr = lineEl.getAttribute('data-value');
+  if (!lineNumberStr) return null;
+  if (lineNumberStr === FILE) return FILE;
+  const lineNumber = Number(lineNumberStr);
+  return Number.isInteger(lineNumber) ? lineNumber : null;
+}