diff --git a/test/lit.cfg b/test/lit.cfg
index 118c979..b69fecc 100644
--- a/test/lit.cfg
+++ b/test/lit.cfg
@@ -207,13 +207,8 @@ def is_preload_disabled():
     if is_windows:
         return True
     elif sys.platform == 'darwin':
-        command = ['csrutil', 'status']
-        pattern = re.compile(r'System Integrity Protection status:\s+enabled')
-        try:
-            output = subprocess.check_output(command, stderr=subprocess.STDOUT)
-            return any(pattern.match(line) for line in output.decode('utf-8').splitlines())
-        except (OSError, subprocess.CalledProcessError):
-            return False
+        # csrutil(8) isn't available in the Nix build sandbox.
+        return True
     else:
         return False
 
@@ -221,6 +216,11 @@ def is_preload_disabled():
 if not is_preload_disabled():
     config.available_features.add('preload')
 
+# Preserve the variables required for the Nix toolchain wrappers.
+for var, value in os.environ.items():
+    if var.startswith('NIX_'):
+        config.environment[var] = value
+
 print(config.substitutions)
 print(config.environment)
 print(config.available_features)