diff --git a/packages/core/src/data-editor/row-grouping-api.ts b/packages/core/src/data-editor/row-grouping-api.ts
index 23eeb8803..988de9013 100644
--- a/packages/core/src/data-editor/row-grouping-api.ts
+++ b/packages/core/src/data-editor/row-grouping-api.ts
@@ -1,13 +1,13 @@
 import React from "react";
 import type { Item } from "../internal/data-grid/data-grid-types.js";
-import { flattenRowGroups, mapRowIndexToPath, type RowGroup, type RowGroupingOptions } from "./row-grouping.js";
+import { flattenRowGroups, mapRowIndexToPath, type RowGroup, type RowGroupingOptions, type MapResult } from "./row-grouping.js";
 
-export type RowGroupingMapperResult<T> = {
+export interface RowGroupingMapperResult<T> extends Omit<MapResult, 'originalIndex'> {
     path: readonly number[];
     originalIndex: T;
     isGroupHeader: boolean;
     groupRows: number;
-};
+}
 
 export type RowGroupingMapper = {
     (itemOrRow: number): RowGroupingMapperResult<number>;
diff --git a/packages/core/src/data-editor/row-grouping.ts b/packages/core/src/data-editor/row-grouping.ts
index c3651d16f..4cda4782b 100644
--- a/packages/core/src/data-editor/row-grouping.ts
+++ b/packages/core/src/data-editor/row-grouping.ts
@@ -167,7 +167,7 @@ export function flattenRowGroups(rowGrouping: RowGroupingOptions, rows: number):
         });
 }
 
-interface MapResult {
+export interface MapResult {
     readonly path: readonly number[];
     readonly isGroupHeader: boolean;
     readonly originalIndex: number;
@@ -202,11 +202,11 @@ export function mapRowIndexToPath(row: number, flattenedRowGroups?: readonly Fla
         if (!group.isCollapsed) {
             if (toGo <= group.rows)
                 return {
-                    path: [...group.path, toGo],
+                    path: [...group.path, toGo - 1],
                     originalIndex: group.headerIndex + toGo,
                     isGroupHeader: false,
-                    groupIndex: toGo,
-                    contentIndex: group.contentIndex + toGo,
+                    groupIndex: toGo - 1,
+                    contentIndex: group.contentIndex + toGo - 1,
                     groupRows: group.rows,
                 };
             toGo = toGo - group.rows - 1;