diff --git a/tests/test_config_api.py b/tests/test_config_api.py
index 00d9521..7498ef8 100644
--- a/tests/test_config_api.py
+++ b/tests/test_config_api.py
@@ -352,6 +352,8 @@ def test_invalid_option():
         PortOption('a', '', allow_zero=False, allow_wellknown=False, allow_registred=False, allow_private=False)
     with raises(ValueError):
         PortOption('a', '', 'tcp:80')
+    with raises(ValueError):
+        PortOption('a', '', '')
     NetworkOption('a', '')
     with raises(ValueError):
         NetworkOption('a', '', 'string')
diff --git a/tiramisu/option/portoption.py b/tiramisu/option/portoption.py
index 7639d19..81bb2ca 100644
--- a/tiramisu/option/portoption.py
+++ b/tiramisu/option/portoption.py
@@ -20,8 +20,6 @@
 # ____________________________________________________________
 """PortOption
 """
-import re
-
 from ..i18n import _
 from .stroption import StrOption
 
@@ -38,7 +36,6 @@ class PortOption(StrOption):
     """
 
     __slots__ = tuple()
-    port_re = re.compile(r"^[0-9]*$")
     _type = "port"
 
     def __init__(
@@ -104,7 +101,7 @@ class PortOption(StrOption):
             value = [value]
 
         for val in value:
-            if not self.port_re.search(val):
+            if not val.isdecimal():
                 raise ValueError()
 
     def second_level_validation(self, value: str, warnings_only: bool) -> None: