diff --git a/ubuntutools/distro_info.py b/ubuntutools/distro_info.py
index d170f8c..6e6b476 100644
--- a/ubuntutools/distro_info.py
+++ b/ubuntutools/distro_info.py
@@ -106,6 +106,10 @@ class DistroInfo(object):
         """Get list of all supported distributions based on the given date."""
         raise NotImplementedError()
 
+    def valid(self, codename):
+        """Check if the given codename is known."""
+        return codename in self.all
+
     def unsupported(self, date=None):
         """Get list of all unsupported distributions based on the given date."""
         if date is None:
@@ -167,6 +171,11 @@ class DebianDistroInfo(DistroInfo):
             raise DistroDataOutdated()
         return distros[-2]["series"]
 
+    def valid(self, codename):
+        """Check if the given codename is known."""
+        return DistroInfo.valid(self, codename) or \
+               codename in ["unstable", "testing", "stable", "old"]
+
 
 class UbuntuDistroInfo(DistroInfo):
     """provides information about Ubuntu's distributions"""
diff --git a/ubuntutools/misc.py b/ubuntutools/misc.py
index 4e41258..8183fab 100644
--- a/ubuntutools/misc.py
+++ b/ubuntutools/misc.py
@@ -177,5 +177,5 @@ def codename_to_distribution(codename):
         if not info:
             continue
 
-        if codename in info().all:
+        if info().valid(codename):
             return distro
diff --git a/ubuntutools/test/test_distro_info.py b/ubuntutools/test/test_distro_info.py
index ee66fc5..7e0a376 100644
--- a/ubuntutools/test/test_distro_info.py
+++ b/ubuntutools/test/test_distro_info.py
@@ -58,6 +58,12 @@ class DebianDistroInfoTestCase(unittest.TestCase):
         """Test: Get latest testing Debian distribution."""
         self.assertEqual(self._distro_info.testing(self._date), "squeeze")
 
+    def test_valid(self):
+        """Test: Check for valid Debian distribution."""
+        self.assertTrue(self._distro_info.valid("sid"))
+        self.assertTrue(self._distro_info.valid("stable"))
+        self.assertFalse(self._distro_info.valid("foobar"))
+
     def test_unsupported(self):
         """Test: List all unsupported Debian distribution."""
         unsupported = ["buzz", "rex", "bo", "hamm", "slink", "potato", "woody",
@@ -111,3 +117,8 @@ class UbuntuDistroInfoTestCase(unittest.TestCase):
                            "gutsy", "intrepid", "jaunty"])
         self.assertEqual(unsupported -
                          set(self._distro_info.unsupported()), set())
+
+    def test_valid(self):
+        """Test: Check for valid Ubuntu distribution."""
+        self.assertTrue(self._distro_info.valid("lucid"))
+        self.assertFalse(self._distro_info.valid("42"))