diff --git a/django/core/validators.py b/django/core/validators.py
index b68fc0ade8..9889fadfd1 100644
--- a/django/core/validators.py
+++ b/django/core/validators.py
@@ -27,6 +27,7 @@ url_re = re.compile(r'^http://\S+$')
 
 from django.conf.settings import JING_PATH
 from django.utils.translation import gettext_lazy, ngettext
+from django.utils.functional import Promise
 
 class ValidationError(Exception):
     def __init__(self, message):
@@ -34,7 +35,7 @@ class ValidationError(Exception):
         if isinstance(message, list):
             self.messages = message
         else:
-            assert isinstance(message, basestring), ("%s should be a string" % repr(message))
+            assert isinstance(message, (basestring, Promise)), ("%s should be a string" % repr(message))
             self.messages = [message]
     def __str__(self):
         # This is needed because, without a __str__(), printing an exception
@@ -49,7 +50,7 @@ class CriticalValidationError(Exception):
         if isinstance(message, list):
             self.messages = message
         else:
-            assert isinstance(message, basestring), ("'%s' should be a string" % message)
+            assert isinstance(message, (basestring, Promise)), ("'%s' should be a string" % message)
             self.messages = [message]
     def __str__(self):
         return str(self.messages)
diff --git a/django/utils/functional.py b/django/utils/functional.py
index f2ea12b1b2..69aeb81850 100644
--- a/django/utils/functional.py
+++ b/django/utils/functional.py
@@ -3,6 +3,14 @@ def curry(*args, **kwargs):
         return args[0](*(args[1:]+moreargs), **dict(kwargs.items() + morekwargs.items()))
     return _curried
 
+class Promise:
+    """
+    This is just a base class for the proxy class created in
+    the closure of the lazy function. It can be used to recognize
+    promises in code.
+    """
+    pass
+
 def lazy(func, *resultclasses):
     """
     Turns any callable into a lazy evaluated callable. You need to give result
@@ -10,7 +18,7 @@ def lazy(func, *resultclasses):
     the lazy evaluation code is triggered. Results are not memoized; the
     function is evaluated on every access.
     """
-    class __proxy__:
+    class __proxy__(Promise):
         # This inner class encapsulates the code that should be evaluated
         # lazily. On calling of one of the magic methods it will force
         # the evaluation and store the result. Afterwards, the result