diff --git a/nixos-infect b/nixos-infect
index d2249c0..0be26dd 100755
--- a/nixos-infect
+++ b/nixos-infect
@@ -192,7 +192,7 @@ infect() {
   # Add nix build users
   # FIXME run only if necessary, rather than defaulting true
   groupadd nixbld -g 30000 || true
-  for i in {1..10}; do useradd -c "Nix build user $i" -d /var/empty -g nixbld -G nixbld -M -N -r -s $(which nologin) nixbld$i || true; done
+  for i in {1..10}; do useradd -c "Nix build user $i" -d /var/empty -g nixbld -G nixbld -M -N -r -s "$(which nologin)" nixbld$i || true; done
   # TODO use addgroup and adduser as fallbacks
   #addgroup nixbld -g 30000 || true
   #for i in {1..10}; do adduser -DH -G nixbld nixbld$i || true; done