diff --git a/src/Forms/TreeDropdownField.php b/src/Forms/TreeDropdownField.php
index 97df4b679..56954f415 100644
--- a/src/Forms/TreeDropdownField.php
+++ b/src/Forms/TreeDropdownField.php
@@ -454,7 +454,13 @@ class TreeDropdownField extends FormField
         $obj = null;
         $sourceObject = $this->getSourceObject();
 
-        Hierarchy::prepopulate_numchildren_cache($sourceObject);
+        // Precache numChildren count if possible.
+        if ($this->getNumChildrenMethod() == 'numChildren') {
+            // We're not calling `Hierarchy::prepopulateTreeDataCache()` because we're not customising results based
+            // on version or Fluent locales. So there would be no performance gain from additional caching.
+            Hierarchy::prepopulate_numchildren_cache($sourceObject);
+        }
+
         if ($id && !$request->requestVar('forceFullTree')) {
             $obj = DataObject::get_by_id($sourceObject, $id);
             $isSubTree = true;