diff --git a/s3fs/tests/test_s3fs.py b/s3fs/tests/test_s3fs.py
index b243ff1f..e59512ce 100644
--- a/s3fs/tests/test_s3fs.py
+++ b/s3fs/tests/test_s3fs.py
@@ -166,6 +166,16 @@ def test_simple(s3):
         assert out == data
 
 
+def test_auto_anon(s3, monkeypatch):
+    monkeypatch.delenv("AWS_ACCESS_KEY_ID")
+    monkeypatch.delenv("AWS_SECRET_ACCESS_KEY")
+    monkeypatch.delenv("AWS_SESSION_TOKEN")
+
+    fs = S3FileSystem(skip_instance_cache=True, endpoint_url=endpoint_uri)
+    fs.s3
+    assert fs.anon
+
+
 def test_with_size(s3):
     data = b"a" * (10 * 2**20)