diff --git a/phpBB/docs/coding-guidelines.html b/phpBB/docs/coding-guidelines.html
index 7843702659..19f005b66b 100644
--- a/phpBB/docs/coding-guidelines.html
+++ b/phpBB/docs/coding-guidelines.html
@@ -1304,6 +1304,7 @@ parent = prosilver</pre>
 </pre></div>
 
 <h4>PHP</h4>
+<p><strong class="error">The use of PHP in HTML files has been deprected in phpBB 3.3 and will be removed in phpBB 4.0.</strong></p>
 <p>A contentious decision has seen the ability to include PHP within the template introduced. This is achieved by enclosing the PHP within relevant tags:</p>
 
 <div class="codebox"><pre>