Index: lib/irb/completion.rb
===================================================================
--- lib/irb/completion.rb	(revision 11833)
+++ lib/irb/completion.rb	(working copy)
@@ -188,7 +188,7 @@
       candidates.grep(/^#{message}/).collect do |e|
 	case e
 	when /^[a-zA-Z_]/
-	  receiver + "." + e
+	  receiver + "." + e.to_s
 	when /^[0-9]/
 	when *Operators
 	  #receiver + " " + e