diff --git a/Makefile b/Makefile
index e470885..30a3a2b 100644
--- a/Makefile
+++ b/Makefile
@@ -3,6 +3,7 @@
 spark: spark/Dockerfile spark/start-master.sh spark/start-worker.sh
 	docker build $(BUILD_OPTS) -t analytics/spark:latest -f $< $@
 
+# Rebuild the following if spark changes!
 pyspark: pyspark/Dockerfile pyspark/kernel.json pyspark/pyspark-kernel.sh
 	docker build $(BUILD_OPTS) -t analytics/pyspark:latest -f $< $@