diff --git a/ftldns/Dockerfile b/ftldns/Dockerfile
index 5018689..742c74f 100644
--- a/ftldns/Dockerfile
+++ b/ftldns/Dockerfile
@@ -6,12 +6,13 @@ FROM alpine:3
 MAINTAINER EasyPi Software Foundation
 
 ARG FTL_VERSION=v5.23
-ARG FTL_URL=https://github.com/pi-hole/FTL/releases/download/$FTL_VERSION/pihole-FTL-musl-linux-x86_64
+ARG FTL_FILE=pihole-FTL-musl-linux-x86_64
+ARG FTL_URL=https://github.com/pi-hole/FTL/releases/download/${FTL_VERSION}/${FTL_FILE}
 
 RUN set -xe \
  && apk add --no-cache curl \
  && echo "conf-dir=/etc/pihole/dnsmasq.d,*.conf" >> /etc/dnsmasq.conf \
- && curl -sSL $FTL_URL -o /usr/bin/pihole-FTL \
+ && curl -sSL ${FTL_URL} -o /usr/bin/pihole-FTL \
  && chmod +x /usr/bin/pihole-FTL \
  && pihole-FTL --version \
  && apk del curl