diff --git a/install.sh b/install.sh
index e60adbe..6a47387 100644
--- a/install.sh
+++ b/install.sh
@@ -234,7 +234,7 @@ if [ -z "${NODEJS_VER:-}" ]; then
   fi
 fi
 
-if [ -n "$NODEJS_VER" ]; then
+if [ -n "${NODEJS_VER:-}" ]; then
   NODEJS_VERT=$(echo ${NODEJS_VER} | cut -c 2- | cut -d '.' -f1)
 
   if [ $NODEJS_VERT -ge 1 ] && [ $NODEJS_VERT -lt 4 ]
@@ -245,7 +245,7 @@ if [ -n "$NODEJS_VER" ]; then
   fi
 fi
 
-if [ -z "$NODEJS_VER" ]; then
+if [ -z "${NODEJS_VER:-}" ]; then
   if [ -n "$(type -p curl)" ]; then
     NODEJS_VER=$(curl -fsL "$NODEJS_BASE_URL/dist/index.tab" | head -n 2 | tail -1 | cut -f 1) \
       || echo 'error automatically determining current node.js version'