diff --git a/rpi23-gen-image.sh b/rpi23-gen-image.sh
index f696e08..a58032c 100755
--- a/rpi23-gen-image.sh
+++ b/rpi23-gen-image.sh
@@ -200,10 +200,10 @@ MISSING_PACKAGES=""
 COMPILER_PACKAGES=""
 
 set +x
-
-#Check if apt-cacher-ng has its default port open on and set APT_PROXY
-if [ -n "$(lsof -i :3142)" ] ; then
-HTTP_PROXY=http://127.0.0.1:3142/
+#Check if apt-cacher-ng has port 3142 open and set APT_PROXY
+APT_CACHER_RUNNING=$(lsof -i :3142 | grep apt-cacher-ng |  cut -d ' ' -f3 | uniq)
+if [ -n ${APT_CACHER_RUNNING} ] ; then
+  APT_PROXY=http://127.0.0.1:3142/
 fi
 
 # Setup architecture specific settings