diff --git a/CHANGES.txt b/CHANGES.txt
index 4dcf826b08..772833264d 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,5 +1,11 @@
 .. _changes_1.5.7:
 
+1.5.8 (unreleased)
+==================
+
+- Ensure that ``pyramid.httpexceptions.exception_response`` returns the
+  appropriate "concreate" class for ``400`` and ``500`` status codes.
+
 1.5.7 (2015-04-28)
 ==================
 
diff --git a/pyramid/httpexceptions.py b/pyramid/httpexceptions.py
index ebee39ada3..6865f6be3b 100644
--- a/pyramid/httpexceptions.py
+++ b/pyramid/httpexceptions.py
@@ -559,10 +559,6 @@ class HTTPClientError(HTTPError):
     a bug.  A server-side traceback is not warranted.  Unless specialized,
     this is a '400 Bad Request'
     """
-    code = 400
-    title = 'Bad Request'
-    explanation = ('The server could not comply with the request since '
-                   'it is either malformed or otherwise incorrect.')
 
 class HTTPBadRequest(HTTPClientError):
     """
@@ -573,7 +569,10 @@ class HTTPBadRequest(HTTPClientError):
 
     code: 400, title: Bad Request
     """
-    pass
+    code = 400
+    title = 'Bad Request'
+    explanation = ('The server could not comply with the request since '
+                   'it is either malformed or otherwise incorrect.')
 
 class HTTPUnauthorized(HTTPClientError):
     """
@@ -925,15 +924,21 @@ class HTTPServerError(HTTPError):
     This is an error condition in which the server is presumed to be
     in-error.  Unless specialized, this is a '500 Internal Server Error'.
     """
+
+class HTTPInternalServerError(HTTPServerError):
+    """
+    subclass of :class:`~HTTPServerError`
+
+    This indicates that the application raised an unexcpected exception.
+    
+    code: 500, title: Internal Server Error
+    """
     code = 500
     title = 'Internal Server Error'
     explanation = (
       'The server has either erred or is incapable of performing '
       'the requested operation.')
 
-class HTTPInternalServerError(HTTPServerError):
-    pass
-
 class HTTPNotImplemented(HTTPServerError):
     """
     subclass of :class:`~HTTPServerError`
diff --git a/pyramid/tests/test_httpexceptions.py b/pyramid/tests/test_httpexceptions.py
index d0779e0808..c700dc80e0 100644
--- a/pyramid/tests/test_httpexceptions.py
+++ b/pyramid/tests/test_httpexceptions.py
@@ -10,13 +10,22 @@ def _callFUT(self, *arg, **kw):
         from pyramid.httpexceptions import exception_response
         return exception_response(*arg, **kw)
 
+    def test_status_400(self):
+        from pyramid.httpexceptions import HTTPBadRequest
+        self.assertTrue(isinstance(self._callFUT(400), HTTPBadRequest))
+
     def test_status_404(self):
         from pyramid.httpexceptions import HTTPNotFound
-        self.assertEqual(self._callFUT(404).__class__, HTTPNotFound)
+        self.assertTrue(isinstance(self._callFUT(404), HTTPNotFound))
+
+    def test_status_500(self):
+        from pyramid.httpexceptions import HTTPInternalServerError
+        self.assertTrue(isinstance(self._callFUT(500),
+                        HTTPInternalServerError))
 
     def test_status_201(self):
         from pyramid.httpexceptions import HTTPCreated
-        self.assertEqual(self._callFUT(201).__class__, HTTPCreated)
+        self.assertTrue(isinstance(self._callFUT(201), HTTPCreated))
 
     def test_extra_kw(self):
         resp = self._callFUT(404,  headers=[('abc', 'def')])