diff --git a/glamor/glamor_transfer.c b/glamor/glamor_transfer.c
index eefeb552b..9efb505f0 100644
--- a/glamor/glamor_transfer.c
+++ b/glamor/glamor_transfer.c
@@ -37,8 +37,8 @@ glamor_upload_boxes(DrawablePtr drawable, BoxPtr in_boxes, int in_nbox,
     PixmapPtr                   pixmap = glamor_get_drawable_pixmap(drawable);
     glamor_pixmap_private       *priv = glamor_get_pixmap_private(pixmap);
     int                         box_index;
-    int                         bytes_per_pixel = drawable->bitsPerPixel >> 3;
     const struct glamor_format *f = glamor_format_for_pixmap(pixmap);
+    int                         bytes_per_pixel = PICT_FORMAT_BPP(f->render_format) >> 3;
     char *tmp_bits = NULL;
 
     if (glamor_drawable_effective_depth(drawable) == 24 && pixmap->drawable.depth == 32)
@@ -145,8 +145,8 @@ glamor_download_boxes(DrawablePtr drawable, BoxPtr in_boxes, int in_nbox,
     PixmapPtr pixmap = glamor_get_drawable_pixmap(drawable);
     glamor_pixmap_private *priv = glamor_get_pixmap_private(pixmap);
     int box_index;
-    int bytes_per_pixel = drawable->bitsPerPixel >> 3;
     const struct glamor_format *f = glamor_format_for_pixmap(pixmap);
+    int bytes_per_pixel = PICT_FORMAT_BPP(f->render_format) >> 3;
 
     glamor_make_current(glamor_priv);