diff --git a/mistral/exceptions.py b/mistral/exceptions.py
index 6dea06416..e854321d3 100644
--- a/mistral/exceptions.py
+++ b/mistral/exceptions.py
@@ -21,96 +21,56 @@ class MistralException(ex.Error):
     """Base Exception for the project
 
     To correctly use this class, inherit from it and define
-    a 'message' and 'code' properties.
+    a 'message' and 'http_code' properties.
     """
     message = "An unknown exception occurred"
-    code = "UNKNOWN_EXCEPTION"
+    http_code = 500
 
     def __str__(self):
         return self.message
 
-    def __init__(self, message=message):
-        self.message = message
+    def __init__(self, message=None):
+        if message is not None:
+            self.message = message
         super(MistralException, self).__init__(
-            '%s: %s' % (self.code, self.message))
+            '%d: %s' % (self.http_code, self.message))
 
 
 class DataAccessException(MistralException):
-    def __init__(self, message=None):
-        super(DataAccessException, self).__init__(message)
-        if message:
-            self.message = message
+    http_code = 400
 
 
 class NotFoundException(MistralException):
+    http_code = 404
     message = "Object not found"
 
-    def __init__(self, message=None):
-        super(NotFoundException, self).__init__(message)
-        if message:
-            self.message = message
-
 
 class DBDuplicateEntry(MistralException):
+    http_code = 409
     message = "Database object already exists"
-    code = "DB_DUPLICATE_ENTRY"
-
-    def __init__(self, message=None):
-        super(DBDuplicateEntry, self).__init__(message)
-        if message:
-            self.message = message
 
 
 class ActionException(MistralException):
-    code = "ACTION_ERROR"
-
-    def __init__(self, message=None):
-        super(MistralException, self).__init__(message)
-        if message:
-            self.message = message
+    http_code = 400
 
 
 class InvalidActionException(MistralException):
-    def __init__(self, message=None):
-        super(InvalidActionException, self).__init__(message)
-        if message:
-            self.message = message
+    http_code = 400
 
 
 class ActionRegistrationException(MistralException):
     message = "Failed to register action"
-    code = "ACTION_REGISTRATION_ERROR"
-
-    def __init__(self, message=None):
-        super(ActionRegistrationException, self).__init__(message)
-        if message:
-            self.message = message
 
 
 class EngineException(MistralException):
-    code = "ENGINE_ERROR"
-
-    def __init__(self, message=None):
-        super(EngineException, self).__init__(message)
-        if message:
-            self.message = message
+    pass
 
 
 class ApplicationContextNotFoundException(MistralException):
+    http_code = 400
     message = "Application context not found"
-    code = "APP_CTX_NOT_FOUND_ERROR"
-
-    def __init__(self, message=None):
-        super(ApplicationContextNotFoundException, self).__init__(message)
-        if message:
-            self.message = message
 
 
 class InvalidModelException(MistralException):
+    http_code = 400
     message = "Wrong entity definition"
-    code = "INVALID_MODEL_EXCEPTION"
-
-    def __init__(self, message=None):
-        super(InvalidModelException, self).__init__(message)
-        if message:
-            self.message = message
diff --git a/mistral/tests/unit/test_exception_base.py b/mistral/tests/unit/test_exception_base.py
new file mode 100644
index 000000000..7dbfc6786
--- /dev/null
+++ b/mistral/tests/unit/test_exception_base.py
@@ -0,0 +1,51 @@
+# -*- encoding: utf-8 -*-
+#
+# Copyright 2014 Rackspace Hosting.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import six
+
+from mistral import exceptions
+from mistral.tests import base
+
+
+class ExceptionTestCase(base.BaseTest):
+    """Test cases for exception code."""
+
+    def test_nf_with_message(self):
+        exc = exceptions.NotFoundException('check_for_this')
+        self.assertIn('check_for_this',
+                      six.text_type(exc))
+        self.assertEqual(exc.http_code, 404)
+
+    def test_nf_with_no_message(self):
+        exc = exceptions.NotFoundException()
+        self.assertIn("Object not found",
+                      six.text_type(exc))
+        self.assertEqual(exc.http_code, 404)
+
+    def test_duplicate_obj_code(self):
+        exc = exceptions.DBDuplicateEntry()
+        self.assertIn("Database object already exists",
+                      six.text_type(exc))
+        self.assertEqual(exc.http_code, 409)
+
+    def test_default_code(self):
+        exc = exceptions.EngineException()
+        self.assertEqual(exc.http_code, 500)
+
+    def test_default_message(self):
+        exc = exceptions.EngineException()
+        self.assertIn("An unknown exception occurred",
+                      six.text_type(exc))