diff --git a/docker/startup.sh b/docker/startup.sh
index 54f541f..19f5b60 100755
--- a/docker/startup.sh
+++ b/docker/startup.sh
@@ -10,11 +10,13 @@ if [ -f "/mnt/$DISK_FILENAME" ]; then
 	[ -w "/mnt/$DISK_FILENAME" ] || { echo "Disk /mnt/$DISK_FILENAME exists and is not writable"; exit 1; }
 	echo "Disk found and is writable."
 else
-  [ -w "/mnt/" ] || { echo "Disk /mnt/$DISK_FILENAME not found and /mnt not writable"; exit 1; }
-  [ -f "/rq0.dsk.gz" ] || { echo "Disk /mnt/$DISK_FILENAME not found and image was not built with a default disk"; exit 1; }
-  echo "Disk not found."
-  echo "Extracting default disk image..."
-  gzip -cd /rq0.dsk.gz > "/mnt/$DISK_FILENAME" || { echo "Failed to extract default disk image to /mnt/$DISK_FILENAME"; exit 1; }
+	[ -w "/mnt/" ] || { echo "Disk /mnt/$DISK_FILENAME not found and /mnt not writable"; exit 1; }
+	[ -f "/rq0.dsk.gz" ] ||
+		{ echo "Disk /mnt/$DISK_FILENAME not found and image was not built with a default disk"; exit 1; }
+	echo "Disk not found."
+	echo "Extracting default disk image..."
+	gzip -cd /rq0.dsk.gz > "/mnt/$DISK_FILENAME" ||
+		{ echo "Failed to extract default disk image to /mnt/$DISK_FILENAME"; exit 1; }
 fi
 
 # Start CoreDNS as soon as possible after validations done
@@ -26,6 +28,8 @@ coredns "$COREDNS_QUIET" -conf /Corefile &
 [ -z "$NOEXIT" ] && EXIT_CMD="exit" || EXIT_CMD=""
 
 echo "Configuring simh..."
+# Allow overriding boot.ini.template
+[ -f /mnt/boot.ini.template ] && cp -f /mnt/boot.ini.template /mnt/boot.ini.template
 sed -e "s/<DISK_FILENAME>/${DISK_FILENAME}/" \
     -e "s/<EXIT>/${EXIT_CMD}/" /boot.ini.template > /boot.ini