diff --git a/src/codecs/ico/decoder.rs b/src/codecs/ico/decoder.rs
index b7fe270996..8876fb3b4f 100644
--- a/src/codecs/ico/decoder.rs
+++ b/src/codecs/ico/decoder.rs
@@ -396,8 +396,8 @@ impl<R: BufRead + Seek> ImageDecoder for IcoDecoder<R> {
                                 }
 
                                 if mask_byte & (1 << bit) != 0 {
-                                    // Set alpha channel to transparent.
-                                    row[x as usize][3] = 0;
+                                    // Set pixel to fully transparent.
+                                    row[x as usize] = [0, 0, 0, 0];
                                 }
 
                                 x += 1;
diff --git a/tests/reference/ico/images/bmp-24bpp-mask.ico.png b/tests/reference/ico/images/bmp-24bpp-mask.ico.png
index 77b763e723..0972df0482 100644
Binary files a/tests/reference/ico/images/bmp-24bpp-mask.ico.png and b/tests/reference/ico/images/bmp-24bpp-mask.ico.png differ
diff --git a/tests/reference/ico/images/bmp-32bpp-alpha.ico.png b/tests/reference/ico/images/bmp-32bpp-alpha.ico.png
index 77b763e723..0972df0482 100644
Binary files a/tests/reference/ico/images/bmp-32bpp-alpha.ico.png and b/tests/reference/ico/images/bmp-32bpp-alpha.ico.png differ