diff --git a/rest_framework/exceptions.py b/rest_framework/exceptions.py
index bc20fcaa3..c46577937 100644
--- a/rest_framework/exceptions.py
+++ b/rest_framework/exceptions.py
@@ -15,6 +15,11 @@ from rest_framework import status
 from rest_framework.utils.serializer_helpers import ReturnDict, ReturnList
 
 
+class SafeReplacerDict(dict):
+    def __missing__(self, key):
+        return key
+
+
 def _get_error_details(data, default_code=None):
     """
     Descend into a nested data structure, forcing any
@@ -144,7 +149,7 @@ class ValidationError(APIException):
     status_code = status.HTTP_400_BAD_REQUEST
     default_detail = _('Invalid input.')
     default_code = 'invalid'
-    default_params = {}
+    default_params = SafeReplacerDict()
 
     def __init__(self, detail=None, code=None, params=None):
         if detail is None:
@@ -157,6 +162,7 @@ class ValidationError(APIException):
         # For validation failures, we may collect many errors together,
         # so the details should always be coerced to a list if not already.
         if isinstance(detail, str):
+            #import pdb; pdb.set_trace()
             detail = [detail % params]
         elif isinstance(detail, ValidationError):
             detail = detail.detail
@@ -166,6 +172,7 @@ class ValidationError(APIException):
                 if isinstance(detail_item, ValidationError):
                     final_detail += detail_item.detail
                 else:
+                    #import pdb; pdb.set_trace()
                     final_detail += [detail_item % params if isinstance(detail_item, str) else detail_item]
             detail = final_detail
         elif not isinstance(detail, dict) and not isinstance(detail, list):
diff --git a/tests/test_validation_error.py b/tests/test_validation_error.py
index 7b8b3190f..39d98d255 100644
--- a/tests/test_validation_error.py
+++ b/tests/test_validation_error.py
@@ -1,3 +1,4 @@
+import pytest
 from django.test import TestCase
 
 from rest_framework import serializers, status
@@ -195,3 +196,20 @@ class TestValidationErrorWithDjangoStyle(TestCase):
         assert str(error.detail[1]) == 'Invalid value: 43'
         assert str(error.detail[2]) == 'Invalid value: 44'
         assert str(error.detail[3]) == 'Invalid value: 45'
+
+    def test_validation_error_without_params(self):
+        """Ensure that substitutable errors can be emitted without params."""
+
+        # mimic the logic in fields.Field.run_validators by saving the exception
+        # detail into a list which will then be the detail for a new ValidationError.
+        # this should not throw a KeyError or a TypeError even though
+        # the string has a substitutable substring ...
+        errors = []
+        try:
+            raise ValidationError('%(user)s')
+        except ValidationError as exc:
+            errors.extend(exc.detail)
+
+        # ensure it raises the correct exception type as an input to a new ValidationError
+        with pytest.raises(ValidationError):
+            raise ValidationError(errors)