diff --git a/language/exceptions.xml b/language/exceptions.xml
index 0018e7825d..3770815c3b 100644
--- a/language/exceptions.xml
+++ b/language/exceptions.xml
@@ -25,6 +25,11 @@
    "<literal>Uncaught Exception ...</literal>" message, unless a handler has
    been defined with <function>set_exception_handler</function>.
   </para>
+  <para>
+   The thrown object must be an instance of the <classname>Exception</classname>
+   class or a subclass of <classname>Exception</classname>. Trying to throw an
+   object that is not will result in a PHP Fatal Error.
+  </para>
   <note>
    <para>
     Internal PHP functions mainly use