diff --git a/activerecord/lib/active_record/associations/class_methods/join_dependency.rb b/activerecord/lib/active_record/associations/class_methods/join_dependency.rb
index 87541e05294fb01dac4573b83e1ef83d4e71832b..7c7fa964f8b8ff9c3616c1d3de9c3c424062260b 100644
--- a/activerecord/lib/active_record/associations/class_methods/join_dependency.rb
+++ b/activerecord/lib/active_record/associations/class_methods/join_dependency.rb
@@ -38,7 +38,7 @@ def columns(connection)
             join_part.column_names_with_alias.collect{ |column_name, aliased_name|
               "#{connection.quote_table_name join_part.aliased_table_name}.#{connection.quote_column_name column_name} AS #{aliased_name}"
             }
-          }.flatten.join(", ")
+          }.flatten
         end
 
         def count_aliases_from_table_joins(name)