diff --git a/build-docker.sh b/build-docker.sh
index 2141451..0329819 100755
--- a/build-docker.sh
+++ b/build-docker.sh
@@ -7,7 +7,8 @@ DOCKER="docker"
 
 # Ensure that any config variables we passed in are written to an env_file
 # so invocations in subsquent shells preserve these values
-printenv | grep 'FWVERSION=\|SERIAL=\|ROOTUSER\|ROOTUSERPASS' > "$DIR/.customvars"
+# Add || true so passing no custom vars doesn't bork up execution
+printenv | grep 'FWVERSION=\|SERIAL=\|ROOTUSER\|ROOTUSERPASS' || true > "$DIR/.customvars"
 
 if ! ${DOCKER} ps >/dev/null 2>&1; then
 	DOCKER="sudo docker"