diff --git a/polygerrit-ui/app/api/diff.ts b/polygerrit-ui/app/api/diff.ts
index 7e619c238e..5d7125cb4a 100644
--- a/polygerrit-ui/app/api/diff.ts
+++ b/polygerrit-ui/app/api/diff.ts
@@ -225,6 +225,9 @@ export declare interface CoverageRange {
   code_range: LineRange;
 }
 
+/** LOST LineNumber is for ported comments without a range, they have their own
+ *  line number and are added on top of the FILE row in gr-diff
+ */
 export declare type LineNumber = number | 'FILE' | 'LOST';
 
 /** The detail of the 'create-comment' event dispatched by gr-diff. */