diff --git a/wx/lib/agw/thumbnailctrl.py b/wx/lib/agw/thumbnailctrl.py
index d0511803..b6af9644 100644
--- a/wx/lib/agw/thumbnailctrl.py
+++ b/wx/lib/agw/thumbnailctrl.py
@@ -506,7 +506,7 @@ class PILImageHandler(object):
         import PIL.ImageEnhance as ImageEnhance
 
         pil = Image.new('RGB', (img.GetWidth(), img.GetHeight()))
-        pil.frombytes(img.GetData())
+        pil.frombytes(bytes(img.GetData()))
         enh = ImageEnhance.Brightness(pil)
         enh = enh.enhance(1.5)
         img.SetData(enh.convert('RGB').tobytes())