diff --git a/reference/misc/functions/define.xml b/reference/misc/functions/define.xml
index 2d7718ddb0..28fbbc4c20 100644
--- a/reference/misc/functions/define.xml
+++ b/reference/misc/functions/define.xml
@@ -52,6 +52,11 @@
        <literal>CONSTANT</literal> and <literal>Constant</literal> represent
        different values.
       </para>
+      <note>
+       <para>
+        Case-insensitive constants are stored as lower-case.
+       </para>
+      </note>
      </listitem>
     </varlistentry>
    </variablelist>