diff --git a/datasets/add_months.sh b/datasets/add_months.sh
index e23b761..8f331c7 100755
--- a/datasets/add_months.sh
+++ b/datasets/add_months.sh
@@ -108,6 +108,7 @@ parallel --joblog add_months_joblog.txt --results add_months_logs \
 # --- Part 2: sort new months into staging (Spark, single fat node) ----------
 
 source "$SPARK_CONF_DIR/spark-env.sh"
+export PYSPARK_PYTHON="$PYTHON"
 start_spark_cluster.sh
 
 spark-submit --master "spark://$(hostname):$SPARK_MASTER_PORT" \