diff --git a/src/calibre/ebooks/mobi/output.py b/src/calibre/ebooks/mobi/output.py
index 49da18ea7b..d82704a0df 100644
--- a/src/calibre/ebooks/mobi/output.py
+++ b/src/calibre/ebooks/mobi/output.py
@@ -41,6 +41,24 @@ class MOBIOutput(OutputFormatPlugin):
         ),
     ])
 
+    def remove_image_transparencies(self):
+        from calibre.utils.magick.draw import save_cover_data_to
+        for item in self.oeb.manifest:
+            if item.media_type.startswith('image'):
+                raw = item.data
+                ext = item.media_type.split('/')[-1].lower()
+                if ext not in ('png', 'gif') or not raw:
+                    continue
+                try:
+                    data = save_cover_data_to(raw, 'img.'+ext, return_data=True)
+                except:
+                    self.log.exception('Failed to remove transparency from',
+                            item.href)
+                    data = None
+                if data is not None:
+                    item.data = data
+                    item.unload_data_from_memory()
+
     def check_for_periodical(self):
         if self.oeb.metadata.publication_type and \
             unicode(self.oeb.metadata.publication_type[0]).startswith('periodical:'):
@@ -160,6 +178,7 @@ class MOBIOutput(OutputFormatPlugin):
         from calibre.ebooks.oeb.transforms.rasterize import SVGRasterizer, Unavailable
         from calibre.ebooks.oeb.transforms.htmltoc import HTMLTOCAdder
         from calibre.customize.ui import plugin_for_input_format
+        self.remove_image_transparencies()
         imagemax = PALM_MAX_IMAGE_SIZE if opts.rescale_images else None
         if not opts.no_inline_toc:
             tocadder = HTMLTOCAdder(title=opts.toc_title)