diff --git a/src/lv_core/lv_obj.c b/src/lv_core/lv_obj.c
index aef953042e..b11bbc8d1e 100644
--- a/src/lv_core/lv_obj.c
+++ b/src/lv_core/lv_obj.c
@@ -1264,7 +1264,10 @@ void lv_obj_set_opa_scale_enable(lv_obj_t * obj, bool en)
 }
 
 /**
- * Set the opa scale of an object
+ * Set the opa scale of an object.
+ * The opacity of this object and all it's children will be scaled down with this factor.
+ * `lv_obj_set_opa_scale_enable(obj, true)` needs to be called to enable it.
+ * (not for all children just for the parent where to start the opa scaling)
  * @param obj pointer to an object
  * @param opa_scale a factor to scale down opacity [0..255]
  */
diff --git a/src/lv_core/lv_obj.h b/src/lv_core/lv_obj.h
index f6cd7b2bbd..cc5bd3d74c 100644
--- a/src/lv_core/lv_obj.h
+++ b/src/lv_core/lv_obj.h
@@ -510,7 +510,10 @@ void lv_obj_set_parent_event(lv_obj_t * obj, bool en);
 void lv_obj_set_opa_scale_enable(lv_obj_t * obj, bool en);
 
 /**
- * Set the opa scale of an object
+ * Set the opa scale of an object.
+ * The opacity of this object and all it's children will be scaled down with this factor.
+ * `lv_obj_set_opa_scale_enable(obj, true)` needs to be called to enable it.
+ * (not for all children just for the parent where to start the opa scaling)
  * @param obj pointer to an object
  * @param opa_scale a factor to scale down opacity [0..255]
  */