http://lists.cairographics.org/archives/cairo/2013-March/024195.html
--- src/cairo-png.c	2012-03-29 12:05:32.000000000 +0200
+++ src/cairo-png.c	2013-03-30 09:13:50.817181600 +0100
@@ -497,6 +497,20 @@
     }
 }
 
+/* branches into premultiply_data or convert_bytes_to_data depending on color type */
+static void read_user_transform_func (png_structp png, png_row_infop row_info, png_bytep data)
+{
+    switch ((cairo_format_t) png_get_user_transform_ptr (png)) {
+        case CAIRO_FORMAT_ARGB32:
+            premultiply_data (png, row_info, data);
+            break;
+
+        case CAIRO_FORMAT_RGB24:
+            convert_bytes_to_data (png, row_info, data);
+            break;
+    }
+}
+
 static cairo_status_t
 stdio_read_func (void *closure, unsigned char *data, unsigned int size)
 {
@@ -623,6 +637,9 @@
 
     png_set_filler (png, 0xff, PNG_FILLER_AFTER);
 
+    /* this must be stored before calling png_read_update_info */
+    png_set_read_user_transform_fn (png, read_user_transform_func);
+
     /* recheck header after setting EXPAND options */
     png_read_update_info (png, info);
     png_get_IHDR (png, info,
@@ -643,15 +660,15 @@
 
 	case PNG_COLOR_TYPE_RGB_ALPHA:
 	    format = CAIRO_FORMAT_ARGB32;
-	    png_set_read_user_transform_fn (png, premultiply_data);
 	    break;
 
 	case PNG_COLOR_TYPE_RGB:
 	    format = CAIRO_FORMAT_RGB24;
-	    png_set_read_user_transform_fn (png, convert_bytes_to_data);
 	    break;
     }
 
+    png_set_user_transform_info (png, (void*) format, 0, 0);
+
     stride = cairo_format_stride_for_width (format, png_width);
     if (stride < 0) {
 	surface = _cairo_surface_create_in_error (_cairo_error (CAIRO_STATUS_INVALID_STRIDE));