diff --git a/tests/test_url_query.py b/tests/test_url_query.py
index 1a7407a..1336fd5 100644
--- a/tests/test_url_query.py
+++ b/tests/test_url_query.py
@@ -65,3 +65,33 @@ def test_path_and_scheme_are_preserved() -> None:
     assert out.startswith("https://example.com:8443/api/v1/foo?")
     parsed = dict(parse_qsl(urlparse(out).query))
     assert parsed == {"token": MASK, "page": "1"}
+
+
+# ── IPv6 host edge cases (issue #4) ──────────────────────────────────────
+
+
+def test_ipv6_loopback_with_port_token_redacted() -> None:
+    """IPv6 loopback with port: token redacted, host/port preserved."""
+    out = redact_url_query("http://[::1]:8080/api?token=abc")
+    assert "abc" not in out
+    parsed = dict(parse_qsl(urlparse(out).query))
+    assert parsed == {"token": MASK}
+    assert "[::1]" in out
+    assert ":8080" in out
+
+
+def test_ipv6_full_address_without_port() -> None:
+    """Full IPv6 address without port: api_key redacted, page preserved."""
+    out = redact_url_query("http://[2001:db8::1]/api?api_key=abc&page=1")
+    assert "abc" not in out
+    parsed = dict(parse_qsl(urlparse(out).query))
+    assert parsed == {"api_key": MASK, "page": "1"}
+
+
+def test_ipv6_no_misparse_brackets() -> None:
+    """IPv6 brackets must not be confused with query delimiters."""
+    out = redact_url_query("http://[fe80::1%25eth0]/path?token=secret")
+    assert "secret" not in out
+    parsed = dict(parse_qsl(urlparse(out).query))
+    assert parsed == {"token": MASK}
+    assert "[fe80::1%25eth0]" in out