diff --git a/Dockerfile b/Dockerfile
index 9c816b0c18..e0a3949517 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,15 +4,15 @@ ARG USER_ID
 ARG GROUP_ID
 ENV DEBIAN_FRONTEND noninteractive
 
-RUN apt-get update && apt-get install -y git cmake make ruby gcc python3 python3-pip gcc-arm-none-eabi
+RUN apt-get update && apt-get install -y git cmake make ruby gcc python3 python3-pip gcc-arm-none-eabi ninja-build
 
 RUN pip install pyyaml
 
 # if either of these are already set the same as the user's machine, leave them be and ignore the error
-RUN addgroup --gid $GROUP_ID inav; exit 0;
-RUN adduser --disabled-password --gecos '' --uid $USER_ID --gid $GROUP_ID inav; exit 0;
+RUN if [ -n "$USER_ID" ]; then RUN addgroup --gid $GROUP_ID inav; exit 0; fi
+RUN if [ -n "$USER_ID" ]; then  RUN adduser --disabled-password --gecos '' --uid $USER_ID --gid $GROUP_ID inav; exit 0; fi
 
-USER inav
+RUN if [ -n "$USER_ID" ]; then USER inav; fi
 RUN git config --global --add safe.directory /src
 
 VOLUME /src