diff --git a/product/ERP5/tests/testERP5Base.py b/product/ERP5/tests/testERP5Base.py
index b598ab1ddb024ffd303fc83b796e7a3d60cfe973..33e704be76f436a7f516af5f8941a3487ba90976 100644
--- a/product/ERP5/tests/testERP5Base.py
+++ b/product/ERP5/tests/testERP5Base.py
@@ -1253,22 +1253,20 @@ class TestERP5Base(ERP5TypeTestCase):
   def test_ConvertImage(self):
     image = self.portal.newContent(portal_type='Image', id='test_image')
     image.edit(file=self.makeImageFileUpload('erp5_logo.png'))
-    image_type, image_data = image.convert('jpg', display='thumbnail')
-    self.assertEquals('image/jpeg', image_type)
-    # magic
-    self.assertEquals('\xff', image_data[0])
-    self.assertEquals('\xd8', image_data[1])
-  
-  def test_ConvertImageQuality(self):
-    image = self.portal.newContent(portal_type='Image', id='test_image')
-    image.edit(file=self.makeImageFileUpload('erp5_logo.png'))
-    image_type, image_data = image.convert('jpg', display='thumbnail',
-                                           quality=100)
-    self.assertEquals('image/jpeg', image_type)
-    # magic
-    self.assertEquals('\xff', image_data[0])
-    self.assertEquals('\xd8', image_data[1])
-  
+    self.assertEqual('image/png', image.getContentType())
+    self.assertEqual((320, 250), (image.getWidth(), image.getHeight()))
+
+    from Products.ERP5Type.Document import newTempImage
+    def convert(**kw):
+      image_type, image_data = image.convert('jpg', display='thumbnail', **kw)
+      self.assertEqual('image/jpeg', image_type)
+      thumbnail = newTempImage(self.portal, 'thumbnail', data=image_data)
+      self.assertEqual(image_type, thumbnail.getContentType())
+      self.assertEqual((128, 100), (thumbnail.getWidth(),
+                                    thumbnail.getHeight()))
+      return thumbnail.getSize()
+    self.assertTrue(convert() < convert(quality=100))
+
   def test_ConvertImagePdata(self):
     image = self.portal.newContent(portal_type='Image', id='test_image')
     image.edit(file=self.makeImageFileUpload('erp5_logo.bmp'))