diff --git a/API.md b/API.md
index 956c6b86..cc874d09 100644
--- a/API.md
+++ b/API.md
@@ -228,7 +228,7 @@ class MyForm extends React.Component {
 }
 ```
 
-With the `preventExternalInvalidation` the input will not be invalidated though it has an error.
+With the `preventExternalInvalidation` the input will not be invalidated though it has an error when `updateInputsWithError()` or an `invalidate` callback is called.
 
 ### <a id="withFormsy">`withFormsy`</a>