1 files changed, 21 insertions, 14 deletions
diff --git a/lib/banzai/filter/syntax_highlight_filter.rb b/lib/banzai/filter/syntax_highlight_filter.rb
index 7da565043d1..a79a0154846 100644
--- a/lib/banzai/filter/syntax_highlight_filter.rb
+++ b/lib/banzai/filter/syntax_highlight_filter.rb
@@ -14,23 +14,26 @@ module Banzai
       end
 
       def highlight_node(node)
-        language = node.attr('lang')
         code = node.text
-        css_classes = "code highlight"
-        lexer = lexer_for(language)
-        lang = lexer.tag
-
-        begin
-          code = Rouge::Formatters::HTMLGitlab.format(lex(lexer, code), tag: lang)
-
-          css_classes << " js-syntax-highlight #{lang}"
-        rescue
-          lang = nil
-          # Gracefully handle syntax highlighter bugs/errors to ensure
-          # users can still access an issue/comment/etc.
+        css_classes = 'code highlight js-syntax-highlight'
+        language = node.attr('lang')
+
+        if use_rouge?(language)
+          lexer = lexer_for(language)
+          language = lexer.tag
+
+          begin
+            code = Rouge::Formatters::HTMLGitlab.format(lex(lexer, code), tag: language)
+            css_classes << " #{language}"
+          rescue
+            # Gracefully handle syntax highlighter bugs/errors to ensure
+            # users can still access an issue/comment/etc.
+
+            language = nil
+          end
         end
 
-        highlighted = %(<pre class="#{css_classes}" lang="#{lang}" v-pre="true"><code>#{code}</code></pre>)
+        highlighted = %(<pre class="#{css_classes}" lang="#{language}" v-pre="true"><code>#{code}</code></pre>)
 
         # Extracted to a method to measure it
         replace_parent_pre_element(node, highlighted)
@@ -51,6 +54,10 @@ module Banzai
         # Replace the parent `pre` element with the entire highlighted block
         node.parent.replace(highlighted)
       end
+
+      def use_rouge?(language)
+        %w(math mermaid plantuml).exclude?(language)
+      end
     end
   end
 end