diff --git a/Dockerfile.ubuntu b/Dockerfile.ubuntu
index 3100da3..ff8f45d 100644
--- a/Dockerfile.ubuntu
+++ b/Dockerfile.ubuntu
@@ -11,7 +11,7 @@ ENV PHP_VERSION=${PHP_VERSION}
 WORKDIR /root
 
 # Use root user to install all dependencies
-USER ROOT
+USER root
 
 RUN apt -y update && apt -y upgrade && apt -y install \
     software-properties-common