diff --git a/setup_system.sh b/setup_system.sh
index 121b358..1f0e444 100755
--- a/setup_system.sh
+++ b/setup_system.sh
@@ -345,6 +345,11 @@ function setup_debian() {
     change_shell || return 13
 }
 
+if [ "$EUID" -eq 0 ]; then
+    echo "Don't run this script as root." 1>&2
+    exit 2
+fi
+
 ID_LIKE="$(grep ID_LIKE= </etc/os-release | cut -d= -f2)"
 
 echo "Setting up ${ID_LIKE^:?}-like OS."
@@ -355,7 +360,7 @@ elif [[ "$ID_LIKE" == "debian" ]]; then
     setup_debian || echo "Setup failed: $?"
 else
     echo "ERROR: Unsupported system: ID_LIKE=$ID_LIKE"
-    exit 2
+    exit 3
 fi
 
 echo "Setup finished."