diff --git a/README.md b/README.md
index 164c8d1..e7f68fc 100644
--- a/README.md
+++ b/README.md
@@ -86,3 +86,4 @@ Planned changes:
 4. Don't enable `gbr` and `argb` features. All pixel types are enabled by default.
 5. In generic code operating on pixels, add `Copy + 'static` bounds to the pixel types and/or their components.
 6. Test your code with `rgb = { version = "0.8.46", features = ["unstable-experimental"] }`, which enables some of the future breaking changes on the older version. This feature flag is only for testing, and will be changed/removed in the future.
+7. Avoid wildcard imports from `rgb::alt::*`, and avoid using `GRAY8`-`GRAYA16` type aliases.
diff --git a/src/legacy/alt.rs b/src/legacy/alt.rs
index 8c35c93..a889ab2 100644
--- a/src/legacy/alt.rs
+++ b/src/legacy/alt.rs
@@ -52,15 +52,19 @@ pub type ARGB16 = crate::Argb<u16>;
 pub type GRB8 = crate::formats::grb::Grb<u8>;
 
 /// 8-bit gray
+#[deprecated(note = "Refer to ::rgb::alt::Gray<u8> directly (this type alias will change in the next major version)")]
 pub type GRAY8 = Gray<u8>;
 
 /// 16-bit gray in machine's native endian
+#[deprecated(note = "Refer to ::rgb::alt::Gray<u16> directly (this type alias will change in the next major version)")]
 pub type GRAY16 = Gray<u16>;
 
 /// 8-bit gray with alpha in machine's native endian
+#[deprecated(note = "Refer to ::rgb::alt::GrayAlpha<u8> directly (this type alias will change in the next major version)")]
 pub type GRAYA8 = GrayAlpha<u8>;
 
 /// 16-bit gray with alpha in machine's native endian
+#[deprecated(note = "Refer to ::rgb::alt::GrayAlpha<u16> directly (this type alias will change in the next major version)")]
 pub type GRAYA16 = GrayAlpha<u16>;
 
 
@@ -234,6 +238,7 @@ impl<T: Copy> From<Gray<T>> for GrayAlpha<T, u16> {
 }
 
 #[test]
+#[allow(deprecated)]
 fn gray() {
     let rgb: crate::RGB<_> = Gray(1).into();
     assert_eq!(rgb.r, 1);