diff --git a/os_config_applier/tests/test_value_type.py b/os_config_applier/tests/test_value_type.py
index c8529c7..db8d8f4 100644
--- a/os_config_applier/tests/test_value_type.py
+++ b/os_config_applier/tests/test_value_type.py
@@ -31,6 +31,8 @@ class ValueTypeTestCase(testtools.TestCase):
     def test_default(self):
         self.assertEqual("foobar",
                          value_types.ensure_type("foobar", "default"))
+        self.assertEqual("x86_64",
+                         value_types.ensure_type("x86_64", "default"))
 
     def test_default_bad(self):
         self.assertRaises(config_exception.ConfigException,
diff --git a/os_config_applier/value_types.py b/os_config_applier/value_types.py
index 3c5274a..2176879 100644
--- a/os_config_applier/value_types.py
+++ b/os_config_applier/value_types.py
@@ -19,7 +19,7 @@ from config_exception import ConfigException
 
 TYPES = {
     "int": "^[0-9]+$",
-    "default": "^[A-Za-z0-9]*$",
+    "default": "^[A-Za-z0-9_]*$",
     "netaddress": "^[A-Za-z0-9/.:-]+$",
     "raw": ""
 }