diff --git a/docs/api/custom-data.md b/docs/api/custom-data.md
index 3c9cb483cf61649cde5a573503c84f0a97b75487..a1f6679ee96837c12baf8de6129ea0377193cf32 100644
--- a/docs/api/custom-data.md
+++ b/docs/api/custom-data.md
@@ -64,4 +64,14 @@ For entities other than the Contact Entity you can use an alternate notation to
 !!! note 
     When retrieving custom data for contact entity, it will only return one value in the case of a multiple custom group set whereas for other entities (e.g. Address, or using the `CustomValue.get` API) you will get all custom data records that relate to the relevant entity
 
-The CustomValue Entity implicitly determines what the `entity_table` variable should be when it is not supplied. If you find that the implicitly is not working out exactly, then specify the `entity_table` key. 
+The CustomValue Entity implicitly determines what the `entity_table` variable should be when it is not supplied. If you find that the implicitly is not working out exactly, then specify the `entity_table` key.
+
+When setting the value of custom data that is of type checkbox or multivalue it is important to note that the options need to be passed in as an array. For example, if you want to set options `a` and `c` of for custom value `2` on `contact` you should do the following
+
+```php
+$result = civicrm_api3(
+  'Contact',
+  'create', 
+  array('id' = 2, 'custom_2' => array('a', 'c'))
+);
+```