diff --git a/nixos/modules/installer/tools/nixos-install.sh b/nixos/modules/installer/tools/nixos-install.sh
index defc46ad2a72..19676f4e7351 100644
--- a/nixos/modules/installer/tools/nixos-install.sh
+++ b/nixos/modules/installer/tools/nixos-install.sh
@@ -83,8 +83,11 @@ if [[ ! -e $NIXOS_CONFIG && -z $system ]]; then
 fi
 
 # A place to drop temporary stuff.
+tmpdir="$(mktemp -d -p $mountPoint)"
 trap "rm -rf $tmpdir" EXIT
-tmpdir="$(mktemp -d)"
+
+# store temporary files on target filesystem by default
+export TMPDIR=${TMPDIR:-$tmpdir}
 
 sub="auto?trusted=1"