diff --git a/activerecord/lib/active_record/relation/merger.rb b/activerecord/lib/active_record/relation/merger.rb
index c08158d38b..530c47d0d0 100644
--- a/activerecord/lib/active_record/relation/merger.rb
+++ b/activerecord/lib/active_record/relation/merger.rb
@@ -107,11 +107,11 @@ module ActiveRecord
         bind_values  = filter_binds(lhs_binds, removed) + rhs_binds
 
         conn = relation.klass.connection
-        bviter = bind_values.each.with_index
+        bv_index = 0
         where_values.map! do |node|
           if Arel::Nodes::Equality === node && Arel::Nodes::BindParam === node.right
-            (column, _), i = bviter.next
-            substitute = conn.substitute_at column, i
+            substitute = conn.substitute_at(bind_values[bv_index].first, bv_index)
+            bv_index += 1
             Arel::Nodes::Equality.new(node.left, substitute)
           else
             node