diff --git a/tests/files/palette_should_be_grayscale.png b/tests/files/palette_should_be_grayscale.png
new file mode 100644
index 00000000..d3b50e0e
Binary files /dev/null and b/tests/files/palette_should_be_grayscale.png differ
diff --git a/tests/files/rgb_should_be_grayscale.png b/tests/files/rgb_should_be_grayscale.png
new file mode 100644
index 00000000..b50aaf13
Binary files /dev/null and b/tests/files/rgb_should_be_grayscale.png differ
diff --git a/tests/files/rgb_should_be_rgb.png b/tests/files/rgb_should_be_rgb.png
new file mode 100644
index 00000000..3f9bdb1a
Binary files /dev/null and b/tests/files/rgb_should_be_rgb.png differ
diff --git a/tests/files/rgba_should_be_grayscale.png b/tests/files/rgba_should_be_grayscale.png
new file mode 100644
index 00000000..318d4012
Binary files /dev/null and b/tests/files/rgba_should_be_grayscale.png differ
diff --git a/tests/files/rgba_should_be_grayscale_alpha.png b/tests/files/rgba_should_be_grayscale_alpha.png
new file mode 100644
index 00000000..bd78424a
Binary files /dev/null and b/tests/files/rgba_should_be_grayscale_alpha.png differ
diff --git a/tests/files/rgba_should_be_rgb.png b/tests/files/rgba_should_be_rgb.png
new file mode 100644
index 00000000..14b16cd3
Binary files /dev/null and b/tests/files/rgba_should_be_rgb.png differ
diff --git a/tests/files/rgba_should_be_rgba.png b/tests/files/rgba_should_be_rgba.png
new file mode 100644
index 00000000..18a49183
Binary files /dev/null and b/tests/files/rgba_should_be_rgba.png differ
diff --git a/tests/oxipng.rs b/tests/oxipng.rs
index 005f78ff..30362bb7 100644
--- a/tests/oxipng.rs
+++ b/tests/oxipng.rs
@@ -358,7 +358,7 @@ fn palette_should_be_grayscale() {
     };
 
     assert!(png.ihdr_data.color_type == png::ColorType::Grayscale);
-    assert!(png.ihdr_data.bit_depth == png::BitDepth::Eight);
+    assert!(png.ihdr_data.bit_depth == png::BitDepth::Four);
 
     let old_png = image::open(&input).unwrap();
     let new_png = image::open(&output).unwrap();