diff --git a/setup b/setup
index 9ddb092..8605fe3 100644
--- a/setup
+++ b/setup
@@ -1,5 +1,7 @@
 #!/bin/sh
 
+set -u
+
 # Install Nix
 curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | \
   sh -s -- install --no-confirm --extra-conf "trusted-users = $(whoami)"
diff --git a/setup.sh b/setup.sh
index 9ddb092..8605fe3 100644
--- a/setup.sh
+++ b/setup.sh
@@ -1,5 +1,7 @@
 #!/bin/sh
 
+set -u
+
 # Install Nix
 curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | \
   sh -s -- install --no-confirm --extra-conf "trusted-users = $(whoami)"