diff --git a/docs/data/data-grid/aggregation/AggregationTreeData.js b/docs/data/data-grid/aggregation/AggregationTreeData.js
index f13b2c299d342..f197c411b1219 100644
--- a/docs/data/data-grid/aggregation/AggregationTreeData.js
+++ b/docs/data/data-grid/aggregation/AggregationTreeData.js
@@ -120,6 +120,13 @@ const columns = [
 
       return new Date(params.value);
     },
+    valueFormatter: (params) => {
+      if (params.value == null) {
+        return '';
+      }
+
+      return params.value.toLocaleString();
+    },
   },
 ];
 
diff --git a/docs/data/data-grid/aggregation/AggregationTreeData.tsx b/docs/data/data-grid/aggregation/AggregationTreeData.tsx
index 78c6456f21f39..b7da82508a3b5 100644
--- a/docs/data/data-grid/aggregation/AggregationTreeData.tsx
+++ b/docs/data/data-grid/aggregation/AggregationTreeData.tsx
@@ -131,6 +131,13 @@ const columns: GridColDef[] = [
 
       return new Date(params.value);
     },
+    valueFormatter: (params) => {
+      if (params.value == null) {
+        return '';
+      }
+
+      return params.value.toLocaleString();
+    },
   },
 ];