diff --git a/Dockerfile b/Dockerfile
index 802161a..d608cfa 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -140,17 +140,22 @@ RUN apt-get update \
 USER $USERNAME
 WORKDIR /home/$USERNAME
 
+# Set environment variables needed by ArduPilot install script
+ENV USER=$USERNAME
+ENV HOME=/home/$USERNAME
+
 # =============================================================================
 # ARDUPILOT SITL
 # =============================================================================
 RUN git clone --recurse-submodules https://github.com/ArduPilot/ardupilot.git /home/$USERNAME/ardupilot
 
 # Install ArduPilot prerequisites (writes to container's bashrc, not host)
+# The -y flag makes it non-interactive
 WORKDIR /home/$USERNAME/ardupilot
-RUN Tools/environment_install/install-prereqs-ubuntu.sh -y
+RUN bash -c "Tools/environment_install/install-prereqs-ubuntu.sh -y"
 
-# Build ArduCopter SITL
-RUN . ~/.profile && ./waf configure --board sitl && ./waf copter
+# Source environment and build ArduCopter SITL
+RUN bash -c "source ~/.profile && ./waf configure --board sitl && ./waf copter"
 
 # =============================================================================
 # ARDUPILOT GAZEBO PLUGIN