diff --git a/wagtail/wagtailcore/tests/test_blocks.py b/wagtail/wagtailcore/tests/test_blocks.py
index 7f4524d95..ced727dad 100644
--- a/wagtail/wagtailcore/tests/test_blocks.py
+++ b/wagtail/wagtailcore/tests/test_blocks.py
@@ -4,7 +4,7 @@ from django import forms
 from django.forms.utils import ErrorList
 from django.core.exceptions import ValidationError
 from django.test import TestCase
-from django.utils.safestring import mark_safe, SafeText
+from django.utils.safestring import mark_safe, SafeData
 
 from wagtail.wagtailcore import blocks
 from wagtail.wagtailcore.models import Page
@@ -272,22 +272,22 @@ class TestRawHTMLBlock(unittest.TestCase):
     def test_get_default_with_fallback_value(self):
         default_value = blocks.RawHTMLBlock().get_default()
         self.assertEqual(default_value, '')
-        self.assertTrue(isinstance(default_value, SafeText))
+        self.assertIsInstance(default_value, SafeData)
 
     def test_get_default_with_none(self):
         default_value = blocks.RawHTMLBlock(default=None).get_default()
         self.assertEqual(default_value, '')
-        self.assertTrue(isinstance(default_value, SafeText))
+        self.assertIsInstance(default_value, SafeData)
 
     def test_get_default_with_empty_string(self):
         default_value = blocks.RawHTMLBlock(default='').get_default()
         self.assertEqual(default_value, '')
-        self.assertTrue(isinstance(default_value, SafeText))
+        self.assertIsInstance(default_value, SafeData)
 
     def test_get_default_with_nonempty_string(self):
         default_value = blocks.RawHTMLBlock(default='<blink>BOOM</blink>').get_default()
         self.assertEqual(default_value, '<blink>BOOM</blink>')
-        self.assertTrue(isinstance(default_value, SafeText))
+        self.assertIsInstance(default_value, SafeData)
 
     def test_serialize(self):
         block = blocks.RawHTMLBlock()
@@ -298,13 +298,13 @@ class TestRawHTMLBlock(unittest.TestCase):
         block = blocks.RawHTMLBlock()
         result = block.to_python('<blink>BOOM</blink>')
         self.assertEqual(result, '<blink>BOOM</blink>')
-        self.assertTrue(isinstance(result, SafeText))
+        self.assertIsInstance(result, SafeData)
 
     def test_render(self):
         block = blocks.RawHTMLBlock()
         result = block.render(mark_safe('<blink>BOOM</blink>'))
         self.assertEqual(result, '<blink>BOOM</blink>')
-        self.assertTrue(isinstance(result, SafeText))
+        self.assertIsInstance(result, SafeData)
 
     def test_render_form(self):
         block = blocks.RawHTMLBlock()
@@ -317,13 +317,13 @@ class TestRawHTMLBlock(unittest.TestCase):
         block = blocks.RawHTMLBlock()
         result = block.value_from_datadict({'rawhtml': '<blink>BOOM</blink>'}, {}, prefix='rawhtml')
         self.assertEqual(result, '<blink>BOOM</blink>')
-        self.assertTrue(isinstance(result, SafeText))
+        self.assertIsInstance(result, SafeData)
 
     def test_clean_required_field(self):
         block = blocks.RawHTMLBlock()
         result = block.clean(mark_safe('<blink>BOOM</blink>'))
         self.assertEqual(result, '<blink>BOOM</blink>')
-        self.assertTrue(isinstance(result, SafeText))
+        self.assertIsInstance(result, SafeData)
 
         with self.assertRaises(ValidationError):
             block.clean(mark_safe(''))
@@ -332,11 +332,11 @@ class TestRawHTMLBlock(unittest.TestCase):
         block = blocks.RawHTMLBlock(required=False)
         result = block.clean(mark_safe('<blink>BOOM</blink>'))
         self.assertEqual(result, '<blink>BOOM</blink>')
-        self.assertTrue(isinstance(result, SafeText))
+        self.assertIsInstance(result, SafeData)
 
         result = block.clean(mark_safe(''))
         self.assertEqual(result, '')
-        self.assertTrue(isinstance(result, SafeText))
+        self.assertIsInstance(result, SafeData)
 
 
 class TestMeta(unittest.TestCase):