diff --git a/setup-node-ubuntu.bash b/setup-node-ubuntu.bash
index 9e3f3a3..45b84b6 100644
--- a/setup-node-ubuntu.bash
+++ b/setup-node-ubuntu.bash
@@ -1,6 +1,14 @@
 #!/bin/bash
 
-if [ -z "$NODE_PATH" ]; then
+set -e
+set -u
+set -o pipefail
+
+if [ -z "${PREFIX-}" ]; then
+  PREFIX=""
+fi
+
+if [ -n "$NODE_PATH" ]; then
   node_install_path=$(dirname $(dirname $NODE_PATH))
 else
   node_install_path=$PREFIX/usr/local