diff --git a/src/core/lv_obj_tree.c b/src/core/lv_obj_tree.c
index 5d72d76dc..d186ad0d3 100644
--- a/src/core/lv_obj_tree.c
+++ b/src/core/lv_obj_tree.c
@@ -339,7 +339,7 @@ uint32_t lv_obj_get_index(const lv_obj_t * obj)
     LV_ASSERT_OBJ(obj, MY_CLASS);
 
     lv_obj_t * parent = lv_obj_get_parent(obj);
-    if(parent == NULL) return 0;
+    if(parent == NULL) return 0xFFFFFFFF;
 
     uint32_t i = 0;
     for(i = 0; i < lv_obj_get_child_cnt(parent); i++) {
diff --git a/src/core/lv_obj_tree.h b/src/core/lv_obj_tree.h
index 4d10c550f..cc4ad3398 100644
--- a/src/core/lv_obj_tree.h
+++ b/src/core/lv_obj_tree.h
@@ -151,7 +151,8 @@ uint32_t lv_obj_get_child_cnt(const struct _lv_obj_t * obj);
  * Get the index of a child.
  * @param obj       pointer to an object
  * @return          the child index of the object.
- *                  E.g. 0: the oldest (firstly created child)
+ *                  E.g. 0: the oldest (firstly created child).
+ *                  (0xFFFFFFFF if child could not be found or no parent exists)
  */
 uint32_t lv_obj_get_index(const struct _lv_obj_t * obj);