diff --git a/openerp/tools/image.py b/openerp/tools/image.py
index eb3600a6652..f8f118e34e2 100644
--- a/openerp/tools/image.py
+++ b/openerp/tools/image.py
@@ -68,7 +68,7 @@ def image_resize_image(base64_source, size=(1024, 1024), encoding='base64', file
         return base64_source
     # create a thumbnail: will resize and keep ratios, then sharpen for better looking result
     image.thumbnail(size, Image.ANTIALIAS)
-    sharpener = ImageEnhance.Sharpness(image.convert('RGB'))
+    sharpener = ImageEnhance.Sharpness(image.convert('RGBA'))
     image = sharpener.enhance(2.0)
     # create a transparent image for background
     background = Image.new('RGBA', size, (255, 255, 255, 0))