diff --git a/elements/rhel-common/pre-install.d/00-rhsm b/elements/rhel-common/pre-install.d/00-rhsm
index 274244a5..3b2f9351 100755
--- a/elements/rhel-common/pre-install.d/00-rhsm
+++ b/elements/rhel-common/pre-install.d/00-rhsm
@@ -5,29 +5,29 @@ set -o pipefail
 
 export DIB_RHSM_USER=${DIB_RHSM_USER:-}
 
-if [ -n "$DIB_RHSM_USER" ] && [ -n "$DIB_RHSM_PASSWORD" ] ; then
+if [ -n "${DIB_RHSM_USER:-}" ] && [ -n "${DIB_RHSM_PASSWORD:-}" ] ; then
     opts="--force"
-    if [[ -n "$DIB_SAT_KEY" ]]; then
+    if [[ -n "${DIB_SAT_KEY:-}" ]]; then
         opts="$opts --activationkey ${DIB_SAT_KEY}"
     else
         opts="$opts --username ${DIB_RHSM_USER} --password ${DIB_RHSM_PASSWORD}"
     fi
-    if [[ -n "$DIB_SAT_URL" ]]; then
-        if [[ "$DIB_REG_TYPE" == "rhn" ]]; then
+    if [[ -n "${DIB_SAT_URL:-}" ]]; then
+        if [[ "${DIB_REG_TYPE:-}" == "rhn" ]]; then
             opts="$opts --serverUrl ${DIB_SAT_URL}"
         else
             opts="$opts --serverurl ${DIB_SAT_URL} --sslCACert /usr/share/rhn/RHN-ORG-TRUSTED-SSL-CERT"
         fi
     fi
-    if [[ -n "$DIB_SAT_CERT_RPM_URL" ]]; then
+    if [[ -n "${DIB_SAT_CERT_RPM_URL:-}" ]]; then
         yum install -y ${DIB_SAT_CERT_RPM_URL}
     fi
-    if [[ "$DIB_REG_TYPE" == "rhn" ]]; then
+    if [[ "${DIB_REG_TYPE:-}" == "rhn" ]]; then
         rhnreg_ks $opts --norhnsd
         sleep 1
         # optional channel required for diskimage-builder dependency
         channels="-a -c rhel-x86_64-server-optional-6"
-        if [[ -n "$DIB_RHN_CHANNELS" ]]; then
+        if [[ -n "${DIB_RHN_CHANNELS:-}" ]]; then
             for chan in $DIB_RHN_CHANNELS; do
                 channels="$channels -a -c $chan"
             done
@@ -38,7 +38,7 @@ if [ -n "$DIB_RHSM_USER" ] && [ -n "$DIB_RHSM_PASSWORD" ] ; then
         subscription-manager register $opts
         # wait a second to ensure consumer certificate is finished writing to disk
         sleep 1
-        if [ -z $DIB_RHSM_POOL ]; then
+        if [ -z ${DIB_RHSM_POOL:-} ]; then
             subscription-manager attach --auto
         else
             subscription-manager attach --pool $DIB_RHSM_POOL
@@ -49,7 +49,7 @@ if [ -n "$DIB_RHSM_USER" ] && [ -n "$DIB_RHSM_PASSWORD" ] ; then
         else
             repos="--enable rhel-6-server-optional-rpms"
         fi
-        if [[ -n "$DIB_RHSM_REPOS" ]]; then
+        if [[ -n "${DIB_RHSM_REPOS:-}" ]]; then
             for repo in $DIB_RHSM_REPOS; do
                 repos="$repos --enable $repo"
             done