diff --git a/phpBB/includes/functions_post.php b/phpBB/includes/functions_post.php
index 8ff2680ab3..8b84a76c87 100644
--- a/phpBB/includes/functions_post.php
+++ b/phpBB/includes/functions_post.php
@@ -72,7 +72,7 @@ function prepare_message($message, $html_on, $bbcode_on, $smile_on, $bbcode_uid
 				for ($i = 0; $i < sizeof($allowed_html_tags); $i++)
 				{
 					$match_tag = trim($allowed_html_tags[$i]);
-					if (preg_match('#^<\/?' . $match_tag . '(?!(.*?)((style)|(on[\w]+?))[\s]*?)#i', $hold_string))
+					if (preg_match('#^<\/?' . $match_tag . '(?!(.*?)((style)|( on[\w]+?[\s]?=))[\s]*?)#i', $hold_string))
 					{
 						$tagallowed = true;
 					}