diff --git a/examples/config/overlord/runtime.properties b/examples/config/overlord/runtime.properties
index f452a7d06d6..9c6a35d9879 100644
--- a/examples/config/overlord/runtime.properties
+++ b/examples/config/overlord/runtime.properties
@@ -13,3 +13,5 @@ druid.indexer.queue.startDelay=PT0M
 druid.indexer.runner.javaOpts="-server -Xmx1g"
 druid.indexer.runner.startPort=8088
 druid.indexer.fork.property.druid.computation.buffer.size=268435456
+druid.indexer.fork.property.druid.processing.numThreads=1
+