diff --git a/src/calibre/ebooks/oeb/base.py b/src/calibre/ebooks/oeb/base.py
index 69b2d67b7a..c7334b1585 100644
--- a/src/calibre/ebooks/oeb/base.py
+++ b/src/calibre/ebooks/oeb/base.py
@@ -1048,6 +1048,22 @@ class Manifest(object):
                 self._data = None
             return property(fget, fset, fdel, doc=doc)
 
+        def unload_data_from_memory(self):
+            if isinstance(self._data, (str, bytes)):
+                from calibre.ptempfile import PersistentTemporaryFile
+                pt = PersistentTemporaryFile('_oeb_base_mem_unloader')
+                pt.write(self._data)
+                pt.close()
+                def loader(*args):
+                    with open(pt.name, 'rb') as f:
+                        ans = f.read()
+                    os.remove(pt.name)
+                    return ans
+                self._loader = loader
+                self._data = None
+
+
+
         def __str__(self):
             data = self.data
             if isinstance(data, etree._Element):
diff --git a/src/calibre/ebooks/oeb/transforms/rescale.py b/src/calibre/ebooks/oeb/transforms/rescale.py
index 980c27d504..a881d1cb67 100644
--- a/src/calibre/ebooks/oeb/transforms/rescale.py
+++ b/src/calibre/ebooks/oeb/transforms/rescale.py
@@ -56,17 +56,21 @@ class RescaleImages(object):
                 scaled, new_width, new_height = fit_image(width, height,
                         page_width, page_height)
                 if scaled:
+                    data = None
                     self.log('Rescaling image from %dx%d to %dx%d'%(
                         width, height, new_width, new_height), item.href)
                     if qt:
                         img = img.scaled(new_width, new_height,
                                 Qt.IgnoreAspectRatio, Qt.SmoothTransformation)
-                        item.data = pixmap_to_data(img)
+                        data = pixmap_to_data(img)
                     else:
                         im = im.resize((int(new_width), int(new_height)), PILImage.ANTIALIAS)
                         of = cStringIO.StringIO()
                         im.convert('RGB').save(of, 'JPEG')
-                        item.data = of.getvalue()
+                        data = of.getvalue()
+                    if data is not None:
+                        item.data = data
+                        item.unload_data_from_memory()