diff --git a/lib/rdoc/markup/to_rdoc.rb b/lib/rdoc/markup/to_rdoc.rb
index 90763ccfdb..cbd99c50d5 100644
--- a/lib/rdoc/markup/to_rdoc.rb
+++ b/lib/rdoc/markup/to_rdoc.rb
@@ -254,7 +254,7 @@ def accept_table header, body, aligns
     end
     aligns = aligns.map do |a|
       case a
-      when nil
+      when nil, :center
         :center
       when :left
         :ljust