diff --git a/imagekit/utils.py b/imagekit/utils.py
index 637433e..2c72185 100644
--- a/imagekit/utils.py
+++ b/imagekit/utils.py
@@ -10,10 +10,11 @@ def img_to_fobj(img, format, **kwargs):
     tmp = tempfile.TemporaryFile()
 
     # Preserve transparency if the image is in Pallette (P) mode.
-    if img.mode == 'P':
+    transparency_formats = ('PNG', 'GIF', )
+    if img.mode == 'P' and format in transparency_formats:
         kwargs['transparency'] = len(img.split()[-1].getcolors())
     else:
-        img.convert('RGB')
+        img = img.convert('RGB')
 
     img.save(tmp, format, **kwargs)
     tmp.seek(0)