diff --git a/plugins/markdown/markdown.php b/plugins/markdown/markdown.php
index 6b4aabf..2f24e41 100644
--- a/plugins/markdown/markdown.php
+++ b/plugins/markdown/markdown.php
@@ -288,7 +288,7 @@ function sanitize_html($description)
             $description);
     }
     $description = preg_replace(
-        '#(<[^>]+)on[a-z]*="?[^ "]*"?#is',
+        '#(<[^>]+\s)on[a-z]*="?[^ "]*"?#is',
         '$1',
         $description);
     return $description;