diff --git a/src/validators/domain.py b/src/validators/domain.py
index 23ae263..384ade0 100644
--- a/src/validators/domain.py
+++ b/src/validators/domain.py
@@ -16,6 +16,7 @@ class _IanaTLD:
     _full_cache: Optional[Set[str]] = None
     # source: https://www.statista.com/statistics/265677
     _popular_cache = {"COM", "ORG", "RU", "DE", "NET", "BR", "UK", "JP", "FR", "IT"}
+    _popular_cache.add("ONION")
 
     @classmethod
     def _retrieve(cls):
diff --git a/tests/test_domain.py b/tests/test_domain.py
index 6d8e867..63342f7 100644
--- a/tests/test_domain.py
+++ b/tests/test_domain.py
@@ -46,6 +46,7 @@ def test_returns_true_on_valid_domain(value: str, rfc_1034: bool, rfc_2782: bool
         ("_example.com", True, False, True),
         ("example_.com", True, False, True),
         ("somerandomexample.xn--fiqs8s", True, False, False),
+        ("somerandomexample.onion", True, False, False),
     ],
 )
 def test_returns_true_on_valid_top_level_domain(