diff --git a/src/lib.rs b/src/lib.rs
index 47a551d..4a85aac 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,5 +1,5 @@
 #![deny(missing_docs)]
-#![cfg_attr(feature = "oibit", feature(optin_builtin_traits))]
+#![cfg_attr(feature = "oibit", feature(auto_traits, negative_impls))]
 
 //! A safe approach to using `#[repr(packed)]` data.
 //!
@@ -9,11 +9,47 @@ use std::mem::{transmute, uninitialized, forget, align_of, size_of};
 use std::ptr::write;
 use std::marker::PhantomData;
 
-/// A marker trait indicating that a type has an alignment of `1`.
-///
-/// In general, only applies to `()`, `bool`, `i8`, `u8`, and any types that
-/// contain only members of these types.
-pub unsafe trait Unaligned { }
+macro_rules! define_marker_trait_unaligned {
+    ([$($auto:ident)?] $($impl:item)*) => {
+        /// A marker trait indicating that a type has an alignment of `1`.
+        ///
+        /// In general, only applies to `()`, `bool`, `i8`, `u8`, and any types that
+        /// contain only members of these types.
+        pub unsafe $($auto)? trait Unaligned { }
+
+        $($impl)*
+    }
+}
+
+#[cfg(not(feature = "oibit"))]
+define_marker_trait_unaligned! { []
+    unsafe impl Unaligned for () { }
+    unsafe impl Unaligned for i8 { }
+    unsafe impl Unaligned for u8 { }
+    unsafe impl Unaligned for bool { }
+}
+
+#[cfg(feature = "oibit")]
+define_marker_trait_unaligned! { [auto]
+    // All primitives except the packed ones listed above
+    impl !Unaligned for char { }
+    impl !Unaligned for f32 { }
+    impl !Unaligned for f64 { }
+    impl !Unaligned for i16 { }
+    impl !Unaligned for u16 { }
+    impl !Unaligned for i32 { }
+    impl !Unaligned for u32 { }
+    impl !Unaligned for i64 { }
+    impl !Unaligned for u64 { }
+    impl !Unaligned for isize { }
+    impl !Unaligned for usize { }
+    impl<T> !Unaligned for *const T { }
+    impl<T> !Unaligned for *mut T { }
+    impl<'a, T> !Unaligned for &'a T { }
+    impl<'a, T> !Unaligned for &'a mut T { }
+}
+
+unsafe impl<T> Unaligned for PhantomData<T> { }
 
 /// A type alias that represents the unaligned type of `T`.
 pub type Un<T> = <T as Aligned>::Unaligned;
@@ -134,42 +170,6 @@ pub unsafe trait Packed: Unaligned {
     fn __assert_unaligned() { }
 }
 
-#[cfg(feature = "oibit")]
-mod impls {
-    use super::Unaligned;
-
-    unsafe impl Unaligned for .. { }
-
-    // All primitives except the packed ones listed below
-    impl !Unaligned for char { }
-    impl !Unaligned for f32 { }
-    impl !Unaligned for f64 { }
-    impl !Unaligned for i16 { }
-    impl !Unaligned for u16 { }
-    impl !Unaligned for i32 { }
-    impl !Unaligned for u32 { }
-    impl !Unaligned for i64 { }
-    impl !Unaligned for u64 { }
-    impl !Unaligned for isize { }
-    impl !Unaligned for usize { }
-    impl<T> !Unaligned for *const T { }
-    impl<T> !Unaligned for *mut T { }
-    impl<'a, T> !Unaligned for &'a T { }
-    impl<'a, T> !Unaligned for &'a mut T { }
-}
-
-#[cfg(not(feature = "oibit"))]
-mod impls {
-    use super::Unaligned;
-
-    unsafe impl Unaligned for () { }
-    unsafe impl Unaligned for i8 { }
-    unsafe impl Unaligned for u8 { }
-    unsafe impl Unaligned for bool { }
-}
-
-unsafe impl<T> Unaligned for PhantomData<T> { }
-
 macro_rules! aligned_assert {
     ($t:ident) => {
         unsafe fn __assert_unaligned() {