diff --git a/Dockerfile.unix b/Dockerfile.unix
index 28e8fa8..2bd8ebb 100644
--- a/Dockerfile.unix
+++ b/Dockerfile.unix
@@ -2,8 +2,9 @@ ARG RUBY_VERSION=3.4.1
 FROM ruby:${RUBY_VERSION}
 ARG USER_ID=1000
 ARG GROUP_ID=1000
-RUN groupadd -g $GROUP_ID app && useradd -u $USER_ID -g app -m app
-USER app
+RUN (getent group $GROUP_ID > /dev/null || groupadd -g $GROUP_ID app) && \
+    (getent passwd $USER_ID > /dev/null || useradd -u $USER_ID -g $GROUP_ID -m app)
+USER $USER_ID:$GROUP_ID
 ARG RAILS_VERSION
 # Install Rails based on the version specified but if not specified, install the latest version.
 RUN if [ -z "$RAILS_VERSION" ] ; then gem install rails ; else gem install rails -v $RAILS_VERSION ; fi