diff --git a/src/flake8/utils.py b/src/flake8/utils.py
index cb195ad..6048132 100644
--- a/src/flake8/utils.py
+++ b/src/flake8/utils.py
@@ -51,7 +51,7 @@ _Token = collections.namedtuple("Token", ("tp", "src"))
 _CODE, _FILE, _COLON, _COMMA, _WS = "code", "file", "colon", "comma", "ws"
 _EOF = "eof"
 _FILE_LIST_TOKEN_TYPES = [
-    (re.compile(r"[A-Z][0-9]*(?=$|\s|,)"), _CODE),
+    (re.compile(r"[A-Z]+[0-9]*(?=$|\s|,)"), _CODE),
     (re.compile(r"[^\s:,]+"), _FILE),
     (re.compile(r"\s*:\s*"), _COLON),
     (re.compile(r"\s*,\s*"), _COMMA),
diff --git a/tests/unit/test_utils.py b/tests/unit/test_utils.py
index 4b70918..dcbf8b8 100644
--- a/tests/unit/test_utils.py
+++ b/tests/unit/test_utils.py
@@ -90,6 +90,11 @@ def test_parse_comma_separated_list(value, expected):
             ['f.py:E,F', 'g.py:G,H'],
             [('f.py', ['E', 'F']), ('g.py', ['G', 'H'])],
         ),
+        # six-digits codes are allowed
+        (
+            'f.py: ABC123',
+            [('f.py', ['ABC123'])],
+        )
     ),
 )
 def test_parse_files_to_codes_mapping(value, expected):