diff --git a/packages/x-data-grid-pro/src/hooks/features/serverSideTreeData/utils.ts b/packages/x-data-grid-pro/src/hooks/features/serverSideTreeData/utils.ts
index 4ac6fff64150e..9ebc120ee6a68 100644
--- a/packages/x-data-grid-pro/src/hooks/features/serverSideTreeData/utils.ts
+++ b/packages/x-data-grid-pro/src/hooks/features/serverSideTreeData/utils.ts
@@ -10,7 +10,8 @@ export function skipFiltering(rowTree: GridRowTreeConfig) {
   for (let i = 0; i < nodes.length; i += 1) {
     const node: any = nodes[i];
     filteredRowsLookup[node.id] = true;
-    filteredChildrenCountLookup[node.id] = node.serverChildrenCount;
+    filteredChildrenCountLookup[node.id] =
+      node.serverChildrenCount !== undefined ? node.serverChildrenCount : -1;
   }
 
   return {
diff --git a/packages/x-data-grid-pro/src/utils/tree/insertDataRowInTree.ts b/packages/x-data-grid-pro/src/utils/tree/insertDataRowInTree.ts
index d0efb73ffb33b..b9ebd6f739545 100644
--- a/packages/x-data-grid-pro/src/utils/tree/insertDataRowInTree.ts
+++ b/packages/x-data-grid-pro/src/utils/tree/insertDataRowInTree.ts
@@ -59,7 +59,7 @@ interface InsertDataRowInTreeParams {
   onDuplicatePath?: GridTreePathDuplicateHandler;
   isGroupExpandedByDefault?: DataGridProProps['isGroupExpandedByDefault'];
   defaultGroupingExpansionDepth: number;
-  serverChildrenCount: number;
+  serverChildrenCount?: number;
   groupsToFetch?: Set<GridRowId>;
 }
 
diff --git a/packages/x-data-grid-pro/src/utils/tree/models.ts b/packages/x-data-grid-pro/src/utils/tree/models.ts
index e10bb7d7ba144..b9daf689647e8 100644
--- a/packages/x-data-grid-pro/src/utils/tree/models.ts
+++ b/packages/x-data-grid-pro/src/utils/tree/models.ts
@@ -8,7 +8,7 @@ export interface RowTreeBuilderGroupingCriterion {
 export interface RowTreeBuilderNode {
   id: GridRowId;
   path: RowTreeBuilderGroupingCriterion[];
-  serverChildrenCount: number;
+  serverChildrenCount?: number;
 }
 
 /**
diff --git a/packages/x-data-grid/src/models/gridRows.ts b/packages/x-data-grid/src/models/gridRows.ts
index 3d876c45aeed0..c9dc3c2c41212 100644
--- a/packages/x-data-grid/src/models/gridRows.ts
+++ b/packages/x-data-grid/src/models/gridRows.ts
@@ -118,7 +118,7 @@ export interface GridDataSourceGroupNode extends GridDataGroupNode {
   /**
    * Number of children this node has on the server. Returns `-1` if unknown.
    */
-  serverChildrenCount: number;
+  serverChildrenCount?: number;
   /**
    * The cached path to be passed on as `groupKey` to the server.
    */