diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 591f126b9..55e56ce39 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -679,11 +679,17 @@ class CharField(Field):
         self.min_length = kwargs.pop('min_length', None)
         super(CharField, self).__init__(**kwargs)
         if self.max_length is not None:
-            message = lazy(self.error_messages['max_length'].format, str)(max_length=self.max_length)
-            self.validators.append(MaxLengthValidator(self.max_length, message=message))
+            message = lazy(
+                self.error_messages['max_length'].format,
+                six.text_type)(max_length=self.max_length)
+            self.validators.append(
+                MaxLengthValidator(self.max_length, message=message))
         if self.min_length is not None:
-            message = lazy(self.error_messages['min_length'].format, str)(min_length=self.min_length)
-            self.validators.append(MinLengthValidator(self.min_length, message=message))
+            message = lazy(
+                self.error_messages['min_length'].format,
+                six.text_type)(min_length=self.min_length)
+            self.validators.append(
+                MinLengthValidator(self.min_length, message=message))
 
     def run_validation(self, data=empty):
         # Test for the empty string here so that it does not get validated,
@@ -824,11 +830,17 @@ class IntegerField(Field):
         self.min_value = kwargs.pop('min_value', None)
         super(IntegerField, self).__init__(**kwargs)
         if self.max_value is not None:
-            message = lazy(self.error_messages['max_value'].format, str)(max_value=self.max_value)
-            self.validators.append(MaxValueValidator(self.max_value, message=message))
+            message = lazy(
+                self.error_messages['max_value'].format,
+                six.text_type)(max_value=self.max_value)
+            self.validators.append(
+                MaxValueValidator(self.max_value, message=message))
         if self.min_value is not None:
-            message = lazy(self.error_messages['min_value'].format, str)(min_value=self.min_value)
-            self.validators.append(MinValueValidator(self.min_value, message=message))
+            message = lazy(
+                self.error_messages['min_value'].format,
+                six.text_type)(min_value=self.min_value)
+            self.validators.append(
+                MinValueValidator(self.min_value, message=message))
 
     def to_internal_value(self, data):
         if isinstance(data, six.text_type) and len(data) > self.MAX_STRING_LENGTH:
@@ -858,11 +870,17 @@ class FloatField(Field):
         self.min_value = kwargs.pop('min_value', None)
         super(FloatField, self).__init__(**kwargs)
         if self.max_value is not None:
-            message = lazy(self.error_messages['max_value'].format, str)(max_value=self.max_value)
-            self.validators.append(MaxValueValidator(self.max_value, message=message))
+            message = lazy(
+                self.error_messages['max_value'].format,
+                six.text_type)(max_value=self.max_value)
+            self.validators.append(
+                MaxValueValidator(self.max_value, message=message))
         if self.min_value is not None:
-            message = lazy(self.error_messages['min_value'].format, str)(min_value=self.min_value)
-            self.validators.append(MinValueValidator(self.min_value, message=message))
+            message = lazy(
+                self.error_messages['min_value'].format,
+                six.text_type)(min_value=self.min_value)
+            self.validators.append(
+                MinValueValidator(self.min_value, message=message))
 
     def to_internal_value(self, data):
         if isinstance(data, six.text_type) and len(data) > self.MAX_STRING_LENGTH:
@@ -906,11 +924,17 @@ class DecimalField(Field):
         super(DecimalField, self).__init__(**kwargs)
 
         if self.max_value is not None:
-            message = lazy(self.error_messages['max_value'].format, str)(max_value=self.max_value)
-            self.validators.append(MaxValueValidator(self.max_value, message=message))
+            message = lazy(
+                self.error_messages['max_value'].format,
+                six.text_type)(max_value=self.max_value)
+            self.validators.append(
+                MaxValueValidator(self.max_value, message=message))
         if self.min_value is not None:
-            message = lazy(self.error_messages['min_value'].format, str)(min_value=self.min_value)
-            self.validators.append(MinValueValidator(self.min_value, message=message))
+            message = lazy(
+                self.error_messages['min_value'].format,
+                six.text_type)(min_value=self.min_value)
+            self.validators.append(
+                MinValueValidator(self.min_value, message=message))
 
     def to_internal_value(self, data):
         """
@@ -1661,8 +1685,11 @@ class ModelField(Field):
         max_length = kwargs.pop('max_length', None)
         super(ModelField, self).__init__(**kwargs)
         if max_length is not None:
-            message = lazy(self.error_messages['max_length'].format, str)(max_length=max_length)
-            self.validators.append(MaxLengthValidator(max_length, message=message))
+            message = lazy(
+                self.error_messages['max_length'].format,
+                six.text_type)(max_length=max_length)
+            self.validators.append(
+                MaxLengthValidator(max_length, message=message))
 
     def to_internal_value(self, data):
         rel = getattr(self.model_field, 'rel', None)