diff --git a/src/languages/ruby.js b/src/languages/ruby.js
index f3fb4a4182..e54ae8751b 100644
--- a/src/languages/ruby.js
+++ b/src/languages/ruby.js
@@ -131,6 +131,7 @@ function(hljs) {
     },
     { // regexp container
       begin: '(' + hljs.RE_STARTERS_RE + '|unless)\\s*',
+      keywords: 'unless',
       contains: [
         IRB_OBJECT,
         {