diff --git a/pyap/source_US/data.py b/pyap/source_US/data.py
index 5eecd33..adb8d88 100644
--- a/pyap/source_US/data.py
+++ b/pyap/source_US/data.py
@@ -1227,7 +1227,7 @@ def not_ending_with_terminating_street_type() -> str:
             (?:
                 (?:
                     (?:
-                        [Bb][Oo][Xx]
+                        [Bb][Oo]?[Xx]
                         |
                         [Pp][Mm][Bb]
                         |
diff --git a/tests/test_parser_us.py b/tests/test_parser_us.py
index 975bb61..b8ddc32 100644
--- a/tests/test_parser_us.py
+++ b/tests/test_parser_us.py
@@ -421,6 +421,7 @@ def test_mail_stop(input, expected):
         ("PO Box # A3656", True),
         ("PO Drawer J", True),
         ("P.O. 9774", True),
+        ("PO BX 451", True),
         # negative assertions
         ("po box108 ", False),
         ("PoBox53485 ", False),