diff --git a/lib/axiom/relation/operation/ungroup.rb b/lib/axiom/relation/operation/ungroup.rb
index <HASH>..<HASH> 100644
--- a/lib/axiom/relation/operation/ungroup.rb
+++ b/lib/axiom/relation/operation/ungroup.rb
@@ -50,7 +50,7 @@ module Axiom
           operand.each do |tuple|
             outer_tuple = tuple.project(@outer)
             tuple[attribute].each do |inner_tuple|
-              yield outer_tuple.extend(header, inner_tuple.to_ary)
+              yield outer_tuple.join(header, inner_tuple)
             end
           end
           self
Change Ungroup#each to join the tuples rather than using extend