diff --git a/sesearch b/sesearch
index 97d5b98..6bd8225 100755
--- a/sesearch
+++ b/sesearch
@@ -77,7 +77,7 @@ rbacrtypes.add_argument("--role_trans", action="append_const",
 
 mlsrtypes = parser.add_argument_group("MLS Rule Types")
 mlsrtypes.add_argument("--range_trans", action="append_const",
-                       const="range_transition", dest="mlsrtypes",
+                       const=setools.MLSRuletype.range_transition, dest="mlsrtypes",
                        help="Search range_transition rules.")
 
 expr = parser.add_argument_group("Expressions")
diff --git a/setools/diff/mlsrules.py b/setools/diff/mlsrules.py
index 80f99b2..beb7517 100644
--- a/setools/diff/mlsrules.py
+++ b/setools/diff/mlsrules.py
@@ -18,6 +18,7 @@
 #
 from collections import defaultdict, namedtuple
 
+from ..policyrep import MLSRuletype
 from .descriptors import DiffResultDescriptor
 from .difference import Difference, SymbolWrapper, Wrapper
 from .mls import RangeWrapper
@@ -51,8 +52,10 @@ class MLSRulesDifference(Difference):
             self._create_mls_rule_lists()
 
         added, removed, matched = self._set_diff(
-                self._expand_generator(self._left_mls_rules["range_transition"], MLSRuleWrapper),
-                self._expand_generator(self._right_mls_rules["range_transition"], MLSRuleWrapper))
+                self._expand_generator(self._left_mls_rules[MLSRuletype.range_transition],
+                                       MLSRuleWrapper),
+                self._expand_generator(self._right_mls_rules[MLSRuletype.range_transition],
+                                       MLSRuleWrapper))
 
         modified = []
 
diff --git a/setools/mlsrulequery.py b/setools/mlsrulequery.py
index f53f7c7..864ecf2 100644
--- a/setools/mlsrulequery.py
+++ b/setools/mlsrulequery.py
@@ -20,6 +20,7 @@ import logging
 
 from .descriptors import CriteriaDescriptor, CriteriaSetDescriptor
 from .mixins import MatchObjClass
+from .policyrep import MLSRuletype
 from .query import PolicyQuery
 from .util import match_indirect_regex, match_range
 
@@ -45,7 +46,7 @@ class MLSRuleQuery(MatchObjClass, PolicyQuery):
                      matching the rule's object class.
     """
 
-    ruletype = CriteriaSetDescriptor(lookup_function="validate_mls_ruletype")
+    ruletype = CriteriaSetDescriptor(enum_class=MLSRuletype)
     source = CriteriaDescriptor("source_regex", "lookup_type_or_attr")
     source_regex = False
     source_indirect = True
diff --git a/setools/policyrep/__init__.py b/setools/policyrep/__init__.py
index 4ef9f0a..5cf4106 100644
--- a/setools/policyrep/__init__.py
+++ b/setools/policyrep/__init__.py
@@ -23,6 +23,7 @@
 
 from . import exception
 from .netcontext import PortconProtocol, PortconRange
+from .mlsrule import MLSRuletype
 from .rbacrule import RBACRuletype
 from .selinuxpolicy import SELinuxPolicy
 from .terule import IoctlSet, TERuletype
diff --git a/setools/policyrep/mlsrule.py b/setools/policyrep/mlsrule.py
index c4f3a3a..d2a7f0a 100644
--- a/setools/policyrep/mlsrule.py
+++ b/setools/policyrep/mlsrule.py
@@ -1,4 +1,5 @@
 # Copyright 2014, 2016, Tresys Technology, LLC
+# Copyright 2016, Chris PeBenito <pebenito@ieee.org>
 #
 # This file is part of SETools.
 #
@@ -23,6 +24,7 @@ from . import qpol
 from . import rule
 from . import typeattr
 from . import mls
+from .util import PolicyEnum
 
 
 def mls_rule_factory(policy, symbol):
@@ -57,10 +59,17 @@ def expanded_mls_rule_factory(original, source, target):
 
 def validate_ruletype(t):
     """Validate MLS rule types."""
-    if t not in ["range_transition"]:
+    try:
+        return MLSRuletype.lookup(t)
+    except KeyError:
         raise exception.InvalidMLSRuleType("{0} is not a valid MLS rule type.".format(t))
 
-    return t
+
+class MLSRuletype(PolicyEnum):
+
+    """An enumeration of MLS rule types."""
+
+    range_transition = 1
 
 
 class MLSRule(rule.PolicyRule):
@@ -70,7 +79,7 @@ class MLSRule(rule.PolicyRule):
     def __str__(self):
         return "{0.ruletype} {0.source} {0.target}:{0.tclass} {0.default};".format(self)
 
-    ruletype = "range_transition"
+    ruletype = MLSRuletype.range_transition
 
     @property
     def source(self):
diff --git a/setools/policyrep/selinuxpolicy.py b/setools/policyrep/selinuxpolicy.py
index 637ca1d..a14d960 100644
--- a/setools/policyrep/selinuxpolicy.py
+++ b/setools/policyrep/selinuxpolicy.py
@@ -603,6 +603,8 @@ class SELinuxPolicy(object):
     @staticmethod
     def validate_mls_ruletype(types):
         """Validate MLS rule types."""
+        warnings.warn("MLS ruletypes have changed to an enumeration.",
+                      DeprecationWarning)
         return mlsrule.validate_ruletype(types)
 
     @staticmethod
diff --git a/setoolsgui/mlsrulemodel.py b/setoolsgui/mlsrulemodel.py
index e2075b0..9534b60 100644
--- a/setoolsgui/mlsrulemodel.py
+++ b/setoolsgui/mlsrulemodel.py
@@ -35,7 +35,7 @@ class MLSRuleTableModel(SEToolsTableModel):
 
             if role == Qt.DisplayRole:
                 if col == 0:
-                    return rule.ruletype
+                    return rule.ruletype.name
                 elif col == 1:
                     return str(rule.source)
                 elif col == 2:
diff --git a/tests/diff.py b/tests/diff.py
index 948c8f5..5c6ca2e 100644
--- a/tests/diff.py
+++ b/tests/diff.py
@@ -20,6 +20,7 @@ import unittest
 from socket import IPPROTO_TCP, IPPROTO_UDP
 
 from setools import SELinuxPolicy, PolicyDifference
+from setools import MLSRuletype as MRT
 from setools import RBACRuletype as RRT
 from setools import TERuletype as TRT
 
@@ -749,11 +750,11 @@ class PolicyDifferenceTest(ValidateRule, unittest.TestCase):
         self.assertEqual(2, len(rules))
 
         # added rule with new type
-        self.validate_rule(rules[0], "range_transition", "added_type", "system", "infoflow4",
+        self.validate_rule(rules[0], MRT.range_transition, "added_type", "system", "infoflow4",
                            "s3")
 
         # added rule with existing types
-        self.validate_rule(rules[1], "range_transition", "rt_added_rule_source",
+        self.validate_rule(rules[1], MRT.range_transition, "rt_added_rule_source",
                            "rt_added_rule_target", "infoflow", "s3")
 
     def test_removed_range_transition_rules(self):
@@ -762,11 +763,11 @@ class PolicyDifferenceTest(ValidateRule, unittest.TestCase):
         self.assertEqual(2, len(rules))
 
         # removed rule with new type
-        self.validate_rule(rules[0], "range_transition", "removed_type", "system", "infoflow4",
+        self.validate_rule(rules[0], MRT.range_transition, "removed_type", "system", "infoflow4",
                            "s1")
 
         # removed rule with existing types
-        self.validate_rule(rules[1], "range_transition", "rt_removed_rule_source",
+        self.validate_rule(rules[1], MRT.range_transition, "rt_removed_rule_source",
                            "rt_removed_rule_target", "infoflow", "s1")
 
     def test_modified_range_transition_rules(self):
@@ -775,7 +776,7 @@ class PolicyDifferenceTest(ValidateRule, unittest.TestCase):
         self.assertEqual(1, len(l))
 
         rule, added_default, removed_default = l[0]
-        self.assertEqual("range_transition", rule.ruletype)
+        self.assertEqual(MRT.range_transition, rule.ruletype)
         self.assertEqual("rt_matched_source", rule.source)
         self.assertEqual("system", rule.target)
         self.assertEqual("infoflow", rule.tclass)
diff --git a/tests/mlsrulequery.py b/tests/mlsrulequery.py
index 816d0ac..545a55a 100644
--- a/tests/mlsrulequery.py
+++ b/tests/mlsrulequery.py
@@ -18,7 +18,7 @@
 import unittest
 
 from setools import SELinuxPolicy, MLSRuleQuery
-from setools.policyrep.exception import InvalidMLSRuleType
+from setools import MLSRuletype as RT
 
 from . import mixins
 
@@ -52,7 +52,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test1s", "test1t", "infoflow", "s0")
+        self.validate_rule(r[0], RT.range_transition, "test1s", "test1t", "infoflow", "s0")
 
     def test_003_source_direct_regex(self):
         """MLS rule query with regex, direct, source match."""
@@ -61,8 +61,8 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 2)
-        self.validate_rule(r[0], "range_transition", "test3s", "test3t", "infoflow", "s1")
-        self.validate_rule(r[1], "range_transition", "test3s", "test3t", "infoflow2", "s2")
+        self.validate_rule(r[0], RT.range_transition, "test3s", "test3t", "infoflow", "s1")
+        self.validate_rule(r[1], RT.range_transition, "test3s", "test3t", "infoflow2", "s2")
 
     def test_005_issue111(self):
         """MLS rule query with attribute source criteria, indirect match."""
@@ -71,8 +71,8 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 2)
-        self.validate_rule(r[0], "range_transition", "test5t1", "test5target", "infoflow", "s1")
-        self.validate_rule(r[1], "range_transition", "test5t2", "test5target", "infoflow7", "s2")
+        self.validate_rule(r[0], RT.range_transition, "test5t1", "test5target", "infoflow", "s1")
+        self.validate_rule(r[1], RT.range_transition, "test5t2", "test5target", "infoflow7", "s2")
 
     def test_010_target_direct(self):
         """MLS rule query with exact, direct, target match."""
@@ -81,8 +81,8 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 2)
-        self.validate_rule(r[0], "range_transition", "test10s", "test10t", "infoflow", "s0")
-        self.validate_rule(r[1], "range_transition", "test10s", "test10t", "infoflow2", "s1")
+        self.validate_rule(r[0], RT.range_transition, "test10s", "test10t", "infoflow", "s0")
+        self.validate_rule(r[1], RT.range_transition, "test10s", "test10t", "infoflow2", "s1")
 
     def test_012_target_direct_regex(self):
         """MLS rule query with regex, direct, target match."""
@@ -91,7 +91,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test12s", "test12aFAIL", "infoflow", "s2")
+        self.validate_rule(r[0], RT.range_transition, "test12s", "test12aFAIL", "infoflow", "s2")
 
     def test_014_issue111(self):
         """MLS rule query with attribute target criteria, indirect match."""
@@ -100,8 +100,8 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 2)
-        self.validate_rule(r[0], "range_transition", "test14source", "test14t1", "infoflow", "s1")
-        self.validate_rule(r[1], "range_transition", "test14source", "test14t2", "infoflow7", "s2")
+        self.validate_rule(r[0], RT.range_transition, "test14source", "test14t1", "infoflow", "s1")
+        self.validate_rule(r[1], RT.range_transition, "test14source", "test14t2", "infoflow7", "s2")
 
     @unittest.skip("Setting tclass to a string is no longer supported.")
     def test_020_class(self):
@@ -110,7 +110,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test20", "test20", "infoflow7", "s1")
+        self.validate_rule(r[0], RT.range_transition, "test20", "test20", "infoflow7", "s1")
 
     def test_021_class_list(self):
         """MLS rule query with object class list match."""
@@ -119,8 +119,8 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 2)
-        self.validate_rule(r[0], "range_transition", "test21", "test21", "infoflow3", "s2")
-        self.validate_rule(r[1], "range_transition", "test21", "test21", "infoflow4", "s1")
+        self.validate_rule(r[0], RT.range_transition, "test21", "test21", "infoflow3", "s2")
+        self.validate_rule(r[1], RT.range_transition, "test21", "test21", "infoflow4", "s1")
 
     def test_022_class_regex(self):
         """MLS rule query with object class regex match."""
@@ -128,8 +128,8 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 2)
-        self.validate_rule(r[0], "range_transition", "test22", "test22", "infoflow5", "s1")
-        self.validate_rule(r[1], "range_transition", "test22", "test22", "infoflow6", "s2")
+        self.validate_rule(r[0], RT.range_transition, "test22", "test22", "infoflow5", "s1")
+        self.validate_rule(r[1], RT.range_transition, "test22", "test22", "infoflow6", "s2")
 
     def test_040_range_exact(self):
         """MLS rule query with context range exact match"""
@@ -137,8 +137,8 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test40", "test40", "infoflow",
-                                 "s40:c1 - s40:c0.c4")
+        self.validate_rule(r[0], RT.range_transition, "test40", "test40", "infoflow",
+                           "s40:c1 - s40:c0.c4")
 
     def test_041_range_overlap1(self):
         """MLS rule query with context range overlap match (equal)"""
@@ -146,7 +146,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test41", "test41", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test41", "test41", "infoflow",
                            "s41:c1 - s41:c1.c3")
 
     def test_041_range_overlap2(self):
@@ -155,7 +155,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test41", "test41", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test41", "test41", "infoflow",
                            "s41:c1 - s41:c1.c3")
 
     def test_041_range_overlap3(self):
@@ -164,7 +164,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test41", "test41", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test41", "test41", "infoflow",
                            "s41:c1 - s41:c1.c3")
 
     def test_041_range_overlap4(self):
@@ -173,7 +173,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test41", "test41", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test41", "test41", "infoflow",
                            "s41:c1 - s41:c1.c3")
 
     def test_041_range_overlap5(self):
@@ -182,7 +182,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test41", "test41", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test41", "test41", "infoflow",
                            "s41:c1 - s41:c1.c3")
 
     def test_042_range_subset1(self):
@@ -191,7 +191,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test42", "test42", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test42", "test42", "infoflow",
                            "s42:c1 - s42:c1.c3")
 
     def test_042_range_subset2(self):
@@ -200,7 +200,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test42", "test42", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test42", "test42", "infoflow",
                            "s42:c1 - s42:c1.c3")
 
     def test_043_range_superset1(self):
@@ -209,7 +209,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test43", "test43", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test43", "test43", "infoflow",
                            "s43:c1 - s43:c1.c3")
 
     def test_043_range_superset2(self):
@@ -218,7 +218,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test43", "test43", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test43", "test43", "infoflow",
                            "s43:c1 - s43:c1.c3")
 
     def test_044_range_proper_subset1(self):
@@ -227,7 +227,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test44", "test44", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test44", "test44", "infoflow",
                            "s44:c1 - s44:c1.c3")
 
     def test_044_range_proper_subset2(self):
@@ -245,7 +245,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test44", "test44", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test44", "test44", "infoflow",
                            "s44:c1 - s44:c1.c3")
 
     def test_044_range_proper_subset4(self):
@@ -255,7 +255,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test44", "test44", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test44", "test44", "infoflow",
                            "s44:c1 - s44:c1.c3")
 
     def test_045_range_proper_superset1(self):
@@ -265,7 +265,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test45", "test45", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test45", "test45", "infoflow",
                            "s45:c1 - s45:c1.c3")
 
     def test_045_range_proper_superset2(self):
@@ -283,7 +283,7 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test45", "test45", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test45", "test45", "infoflow",
                            "s45:c1 - s45:c1.c3")
 
     def test_045_range_proper_superset4(self):
@@ -293,10 +293,10 @@ class MLSRuleQueryTest(mixins.ValidateRule, unittest.TestCase):
 
         r = sorted(q.results())
         self.assertEqual(len(r), 1)
-        self.validate_rule(r[0], "range_transition", "test45", "test45", "infoflow",
+        self.validate_rule(r[0], RT.range_transition, "test45", "test45", "infoflow",
                            "s45:c1 - s45:c1.c3")
 
     def test_900_invalid_ruletype(self):
         """MLS rule query with invalid rule type."""
-        with self.assertRaises(InvalidMLSRuleType):
-            q = MLSRuleQuery(self.p, ruletype="type_transition")
+        with self.assertRaises(KeyError):
+            q = MLSRuleQuery(self.p, ruletype=["type_transition"])
diff --git a/tests/policyrep/mlsrule.py b/tests/policyrep/mlsrule.py
index 51b94a6..6ad3781 100644
--- a/tests/policyrep/mlsrule.py
+++ b/tests/policyrep/mlsrule.py
@@ -22,6 +22,7 @@ try:
 except ImportError:
     from mock import Mock, patch
 
+from setools import MLSRuletype as MRT
 from setools.policyrep.qpol import qpol_policy_t, qpol_range_trans_t
 from setools.policyrep.mlsrule import mls_rule_factory, validate_ruletype
 from setools.policyrep.exception import InvalidMLSRuleType, RuleNotConditional
@@ -34,7 +35,7 @@ class MLSRuleTest(unittest.TestCase):
 
     def mock_rangetrans_factory(self, source, target, tclass, default):
         mock_rule = Mock(qpol_range_trans_t)
-        mock_rule.rule_type.return_value = "range_transition"
+        mock_rule.rule_type.return_value = MRT.range_transition
         mock_rule.source_type.return_value = source
         mock_rule.target_type.return_value = target
         mock_rule.object_class.return_value = tclass
@@ -52,8 +53,9 @@ class MLSRuleTest(unittest.TestCase):
 
     def test_001_validate_ruletype(self):
         """RangeTransition valid rule types."""
-        self.assertEqual("range_transition", validate_ruletype("range_transition"))
+        self.assertEqual(MRT.range_transition, validate_ruletype("range_transition"))
 
+    @unittest.skip("MLS ruletype changed to an enumeration.")
     def test_002_validate_ruletype_invalid(self):
         """RangeTransition valid rule types."""
         with self.assertRaises(InvalidMLSRuleType):
@@ -62,7 +64,7 @@ class MLSRuleTest(unittest.TestCase):
     def test_010_ruletype(self):
         """RangeTransition rule type"""
         rule = self.mock_rangetrans_factory("a", "b", "c", "d")
-        self.assertEqual("range_transition", rule.ruletype)
+        self.assertEqual(MRT.range_transition, rule.ruletype)
 
     def test_020_source_type(self):
         """RangeTransition source type"""