diff --git a/scripts/wsrep_sst_common.sh b/scripts/wsrep_sst_common.sh
index bb91eeaeba2..c421bbfdc64 100644
--- a/scripts/wsrep_sst_common.sh
+++ b/scripts/wsrep_sst_common.sh
@@ -129,8 +129,8 @@ done
 readonly WSREP_SST_OPT_BYPASS
 readonly WSREP_SST_OPT_BINLOG
 
-if [ -n "$WSREP_SST_OPT_ADDR_PORT" ]; then
-  if [ -n "$WSREP_SST_OPT_PORT" ]; then
+if [ -n "${WSREP_SST_OPT_ADDR_PORT:-}" ]; then
+  if [ -n "${WSREP_SST_OPT_PORT:-}" ]; then
     if [ "$WSREP_SST_OPT_PORT" != "$WSREP_SST_OPT_ADDR_PORT" ]; then
       wsrep_log_error "port in --port=$WSREP_SST_OPT_PORT differs from port in --address=$WSREP_SST_OPT_ADDR"
       exit 2