diff --git a/lib/redmine/wiki_formatting/textile/redcloth3.rb b/lib/redmine/wiki_formatting/textile/redcloth3.rb
index f0595f438..a2b53997f 100644
--- a/lib/redmine/wiki_formatting/textile/redcloth3.rb
+++ b/lib/redmine/wiki_formatting/textile/redcloth3.rb
@@ -1214,9 +1214,9 @@ class RedCloth3 < String
             all, tag, close = $1, $2, $3
 
             if close.present? && (ALLOWED_TAGS.include?(tag) || (tag =~ /\Aredpre#\d+\z/))
-                "<#{all}#{close}"
+                "<#{htmlesc all}#{close}"
             else
-                "&lt;#{all}#{'&gt;' unless close.blank?}"
+                "&lt;#{htmlesc all}#{'&gt;' unless close.blank?}"
             end
         end
     end
diff --git a/test/helpers/application_helper_test.rb b/test/helpers/application_helper_test.rb
index ddc55dcb8..a9e3b3a74 100644
--- a/test/helpers/application_helper_test.rb
+++ b/test/helpers/application_helper_test.rb
@@ -1296,12 +1296,13 @@ class ApplicationHelperTest < Redmine::HelperTest
   def test_html_tags
     to_test = {
       "<div>content</div>" => "<p>&lt;div&gt;content&lt;/div&gt;</p>",
-      "<div class=\"bold\">content</div>" => "<p>&lt;div class=\"bold\"&gt;content&lt;/div&gt;</p>",
+      "<div class=\"bold\">content</div>" => "<p>&lt;div class=&quot;bold&quot;&gt;content&lt;/div&gt;</p>",
       "<script>some script;</script>" => "<p>&lt;script&gt;some script;&lt;/script&gt;</p>",
       # do not escape pre/code tags
       "<pre>\nline 1\nline2</pre>" => "<pre>\nline 1\nline2</pre>",
       "<pre><code>\nline 1\nline2</code></pre>" => "<pre><code>\nline 1\nline2</code></pre>",
-      "<pre><div>content</div></pre>" => "<pre>&lt;div&gt;content&lt;/div&gt;</pre>",
+      "<pre><div class=\"foo\">content</div></pre>" => "<pre>&lt;div class=\"foo\"&gt;content&lt;/div&gt;</pre>",
+      "<pre><div class=\"<foo\">content</div></pre>" => "<pre>&lt;div class=\"&lt;foo\"&gt;content&lt;/div&gt;</pre>",
       "<!-- opening comment" => "<p>&lt;!-- opening comment</p>",
       # remove attributes including class
       "<pre class='foo'>some text</pre>" => "<pre>some text</pre>",