diff --git a/macros/sql/union.sql b/macros/sql/union.sql
index a5e04c01..46bc22d2 100644
--- a/macros/sql/union.sql
+++ b/macros/sql/union.sql
@@ -1,4 +1,4 @@
-{%- macro union_relations(relations, column_override=none, include=[], exclude=[], source_column_name=none) -%}
+{%- macro union_relations(relations, column_override=none, include=[], exclude=[], source_column_name='_dbt_source_relation') -%}
 
     {%- if exclude and include -%}
         {{ exceptions.raise_compiler_error("Both an exclude and include list were provided to the `union` macro. Only one is allowed") }}
@@ -10,7 +10,6 @@
     {% endif -%}
 
     {%- set column_override = column_override if column_override is not none else {} -%}
-    {%- set source_column_name = source_column_name if source_column_name is not none else '_dbt_source_relation' -%}
 
     {%- set relation_columns = {} -%}
     {%- set column_superset = {} -%}