diff --git a/creditcard/card.py b/creditcard/card.py
index 9d38418..83c20e4 100644
--- a/creditcard/card.py
+++ b/creditcard/card.py
@@ -1,7 +1,8 @@
 import re
+from functools import cached_property
 
+from . import luhn
 from .exceptions import BrandNotFound
-from .luhn import Luhn
 from .utils import sanitize
 
 BRAND_REGEX = {
@@ -69,11 +70,23 @@ class CreditCard:
     def __init__(self, number):
         self.number = sanitize(number)
 
-    def is_valid(self):
-        return all([len(self.number) in range(13, 19), Luhn.checkdigit(self.number)])
-
-    def get_brand(self):
+    @cached_property
+    def _brand(self):
         for brand, regex in BRAND_REGEX.items():
             if re.match(regex, self.number):
                 return brand
+        return None
+
+    def is_valid(self):
+        if not self.number.isdigit():
+            return False
+
+        if self._brand == "softnex":
+            return len(self.number) == 16 and luhn.check_softnex(self.number)
+
+        return len(self.number) in range(13, 19) and luhn.check(self.number)
+
+    def get_brand(self):
+        if brand := self._brand:
+            return brand
         raise BrandNotFound("Card number does not match any brand")
diff --git a/creditcard/luhn.py b/creditcard/luhn.py
index 9a1b5a3..9211a76 100644
--- a/creditcard/luhn.py
+++ b/creditcard/luhn.py
@@ -1,18 +1,31 @@
-class Luhn:
-    @classmethod
-    def checkdigit(cls, card_number):
-        """ checks to make sure that the card passes a luhn mod-10 checksum """
-        _sum = 0
-        num_digits = len(card_number)
-        oddeven = num_digits & 1
-        for i in range(0, num_digits):
-            try:
-                digit = int(card_number[i])
-            except ValueError:
-                return False
-            if not ((i & 1) ^ oddeven):
-                digit = digit * 2
-            if digit > 9:
-                digit = digit - 9
-            _sum = _sum + digit
-        return (_sum % 10) == 0
+def sum_digits(digits):
+    total = 0
+    for i, digit in enumerate(digits, start=1):
+        # Se o índice (iniciando em 1) for ímpar, o valor do dígito é o dígito
+        # original multiplicado por dois, com os dígitos resultantes somados,
+        # o que equivale a subtrair 9 se o valor for maior que 9.
+        # Se for par, o próprio dígito é utilizado, que já está entre 0 e 9.
+        d = int(digit)
+        if i % 2 == 1:
+            d *= 2
+            if d > 9:
+                d -= 9
+        total += d
+    return total
+
+
+def check(digits):
+    total = sum_digits(digits)
+    return total % 10 == 0
+
+
+def check_softnex(digits):
+    total = sum_digits(digits[:15])
+    # A Softnex diverge do Luhn tradicional no cálculo do último dígito.
+    # Enquanto o Luhn apenas requer que a soma em módulo 10 seja 0, a Softnex
+    # modifica o dígito para 1 se o mesmo for 0, o que faz com que o Luhn recuse
+    # o número resultante.
+    dv = 10 - total % 10
+    if dv > 9:
+        dv = 1
+    return int(digits[-1]) == dv
diff --git a/pytest.ini b/pytest.ini
index f108fda..07f742c 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -2,5 +2,4 @@
 norecursedirs = .git
 testpaths = ./tests
 pythonpaths = . ./creditcard
-addopts = --flake8 --cov=creditcard -vv
-flake8-max-line-length = 88
+addopts = --cov=creditcard -vv
diff --git a/tests/unit/test_card.py b/tests/unit/test_card.py
index b414971..2e3aa00 100644
--- a/tests/unit/test_card.py
+++ b/tests/unit/test_card.py
@@ -21,6 +21,11 @@ def test_is_valid(self):
         card = CreditCard("0000000000000a")
         assert card.is_valid() is False
 
+        # Cartão Softnex que não é válido pelo Luhn, mas deve ser aceito pelo
+        # algoritmo específico
+        card = CreditCard("6108000000000041")
+        assert card.is_valid() is True
+
     @pytest.mark.parametrize(
         "brand, number",
         [
diff --git a/tests/unit/test_luhn.py b/tests/unit/test_luhn.py
index 6301487..fecc6d0 100644
--- a/tests/unit/test_luhn.py
+++ b/tests/unit/test_luhn.py
@@ -1,9 +1,31 @@
-from creditcard.luhn import Luhn
+import pytest
+
+from creditcard import luhn
 
 
 class TestLuhn:
-    def test_checkdigit(self):
-        assert Luhn.checkdigit('4539578763621486') is True
-        assert Luhn.checkdigit('5369835519963014') is True
-        assert Luhn.checkdigit('30346836403940') is True
-        assert Luhn.checkdigit('3034683640394a') is False
+    @pytest.mark.parametrize(
+        "number,expected",
+        [
+            ("4539578763621486", True),
+            ("5369835519963014", True),
+            ("5369835519963013", False),
+            ("30346836403940", True),
+            ("6108000158537041", True),
+            ("6108000000000041", False),
+            ("6108000000000040", True),
+        ],
+    )
+    def test_check(self, number, expected):
+        assert luhn.check(number) is expected
+
+    @pytest.mark.parametrize(
+        "number,expected",
+        [
+            ("6108000158537041", True),
+            ("6108000000000041", True),
+            ("6108000000000040", False),
+        ],
+    )
+    def test_check_softnex(self, number, expected):
+        assert luhn.check_softnex(number) is expected