diff --git a/README.md b/README.md
index 4b5dc4e95..890c5cc48 100644
--- a/README.md
+++ b/README.md
@@ -127,7 +127,7 @@ The following configurations can be supplied to models run with the dbt-spark pl
 **Incremental Models**
 
 To use incremental models, specify a `partition_by` clause in your model config. The default incremental strategy used is `insert_overwrite`, which will overwrite the partitions included in your query. Be sure to re-select _all_ of the relevant
-data for a partition when using the `insert_overwrite` strategy.
+data for a partition when using the `insert_overwrite` strategy. If a `partition_by` config is not specified, dbt will overwrite the entire table as an atomic operation, replacing it with new data of the same schema. This is analogous to `truncate` + `insert`.
 
 ```
 {{ config(
diff --git a/dbt/include/spark/macros/materializations/incremental.sql b/dbt/include/spark/macros/materializations/incremental.sql
index f5d7335fb..000659a8f 100644
--- a/dbt/include/spark/macros/materializations/incremental.sql
+++ b/dbt/include/spark/macros/materializations/incremental.sql
@@ -100,9 +100,11 @@
     {% do dbt_spark_validate_merge(file_format) %}
   {% endif %}
 
-  {% call statement() %}
-    set spark.sql.sources.partitionOverwriteMode = DYNAMIC
-  {% endcall %}
+  {% if config.get('partition_by') %}
+    {% call statement() %}
+      set spark.sql.sources.partitionOverwriteMode = DYNAMIC
+    {% endcall %}
+  {% endif %}
 
   {% call statement() %}
     set spark.sql.hive.convertMetastoreParquet = false