diff --git a/language/constants.xml b/language/constants.xml
index 7d68dd2d42..e5bb26d5fe 100644
--- a/language/constants.xml
+++ b/language/constants.xml
@@ -168,6 +168,16 @@ echo CONSTANT;
     </example>
    </para>
 
+   <note>
+    <para>
+     As opposed to defining constants using <function>define</function>,
+     constants defined using the <literal>const</literal> keyword must be
+     declared at the top-level scope because they are defined at compile-time.
+     This means that they cannot be declared inside functions, loops or
+     <literal>if</literal> statements.
+    </para>
+   </note>
+
    <simpara>
     See also <link linkend="language.oop5.constants">Class Constants</link>.
    </simpara>