diff --git a/src/libutil/error.cc b/src/libutil/error.cc
index 027f0b1a5..f57e3ef7d 100644
--- a/src/libutil/error.cc
+++ b/src/libutil/error.cc
@@ -133,7 +133,7 @@ static std::string indent(std::string_view indentFirst, std::string_view indentR
 /**
  * A development aid for finding missing positions, to improve error messages. Example use:
  *
- *     NIX_DEVELOPER_SHOW_UNKNOWN_LOCATIONS=1 _NIX_TEST_ACCEPT=1 make tests/lang.sh.test
+ *     NIX_DEVELOPER_SHOW_UNKNOWN_LOCATIONS=1 _NIX_TEST_ACCEPT=1 just test --suite installcheck -v functional-lang
  *     git diff -U20 tests
  *
  */
diff --git a/tests/functional/lang.sh b/tests/functional/lang.sh
index 59db10340..ca54fb88d 100755
--- a/tests/functional/lang.sh
+++ b/tests/functional/lang.sh
@@ -155,7 +155,7 @@ else
         echo ''
         echo 'You can rerun this test with:'
         echo ''
-        echo '    _NIX_TEST_ACCEPT=1 make tests/functional/lang.sh.test'
+        echo '    _NIX_TEST_ACCEPT=1 just test --suite installcheck -v functional-lang'
         echo ''
         echo 'to regenerate the files containing the expected output,'
         echo 'and then view the git diff to decide whether a change is'
diff --git a/tests/unit/meson.build b/tests/unit/meson.build
index 8b0c66dd8..04fdf62a7 100644
--- a/tests/unit/meson.build
+++ b/tests/unit/meson.build
@@ -12,7 +12,11 @@
 # It's only ~200 lines; better to just refactor the tests themselves which we'll want to do anyway.
 
 default_test_env = {
-  'ASAN_OPTIONS': 'detect_leaks=0:halt_on_error=1:abort_on_error=1:print_summary=1:dump_instruction_bytes=1'
+  'ASAN_OPTIONS': 'detect_leaks=0:halt_on_error=1:abort_on_error=1:print_summary=1:dump_instruction_bytes=1',
+  # Prevents loading global configuration file in /etc/nix/nix.conf in tests 😱
+  'NIX_CONF_DIR': '/var/empty',
+  # Prevent loading user configuration files in tests
+  'NIX_USER_CONF_FILES': '',
 }
 
 libutil_test_support_sources = files(