diff --git a/tests/functional/flakes/run.sh b/tests/functional/flakes/run.sh
index 61af6049a00..6efdd673b81 100755
--- a/tests/functional/flakes/run.sh
+++ b/tests/functional/flakes/run.sh
@@ -37,11 +37,13 @@ env > $TEST_ROOT/expected-env
 nix run -f shell-hello.nix env > $TEST_ROOT/actual-env
 # Remove/reset variables we expect to be different.
 # - PATH is modified by nix shell
+# - we unset TMPDIR on macOS if it contains /var/folders. bad. https://github.com/NixOS/nix/issues/7731
 # - _ is set by bash and is expected to differ because it contains the original command
 # - __CF_USER_TEXT_ENCODING is set by macOS and is beyond our control
 sed -i \
   -e 's/PATH=.*/PATH=.../' \
   -e 's/_=.*/_=.../' \
+  -e '/^TMPDIR=\/var\/folders\/.*/d' \
   -e '/^__CF_USER_TEXT_ENCODING=.*$/d' \
   $TEST_ROOT/expected-env $TEST_ROOT/actual-env
 sort $TEST_ROOT/expected-env | uniq > $TEST_ROOT/expected-env.sorted