diff --git a/tests/functional/check.sh b/tests/functional/check.sh
index 87fb5e245..241810f6b 100644
--- a/tests/functional/check.sh
+++ b/tests/functional/check.sh
@@ -37,6 +37,9 @@ if checkBuildTempDirRemoved $TEST_ROOT/log; then false; fi
 test_custom_build_dir() {
   local customBuildDir="$TEST_ROOT/custom-build-dir"
 
+  # Nix does not create the parent directories, and perhaps it shouldn't try to
+  # decide the permissions of build-dir.
+  mkdir "$customBuildDir"
   nix-build check.nix -A failed --argstr checkBuildId $checkBuildId \
       --no-out-link --keep-failed --option build-dir "$TEST_ROOT/custom-build-dir" 2> $TEST_ROOT/log || status=$?
   [ "$status" = "100" ]