diff --git a/doc/rdoc/markup_reference.rb b/doc/rdoc/markup_reference.rb
index 66ec6786c0..27018c0beb 100644
--- a/doc/rdoc/markup_reference.rb
+++ b/doc/rdoc/markup_reference.rb
@@ -66,7 +66,7 @@
 # In a multi-line comment,
 # \RDoc looks for the comment's natural left margin,
 # which becomes the <em>base margin</em> for the comment
-# and is the initial <em>current margin</em> for for the comment.
+# and is the initial <em>current margin</em> for the comment.
 #
 # The current margin can change, and does so, for example in a list.
 #