diff --git a/README.md b/README.md
index 9846eab..76d486b 100644
--- a/README.md
+++ b/README.md
@@ -88,7 +88,7 @@
 FROM jenkins
 # if we want to install via apt
 USER root
-RUN apt-get install -y ruby make more-thing-here
+RUN apt-get update && apt-get install -y ruby make more-thing-here
 USER jenkins # drop back to the regular jenkins user - good practice
 ```