diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs
index 856d05aa60f1..eedab0be1eff 100644
--- a/rust/kernel/alloc/kbox.rs
+++ b/rust/kernel/alloc/kbox.rs
@@ -401,12 +401,17 @@ where
 }
 
 // SAFETY: The pointer returned by `into_foreign` comes from a well aligned
-// pointer to `T`.
+// pointer to `T` allocated by `A`.
 unsafe impl<T: 'static, A> ForeignOwnable for Box<T, A>
 where
     A: Allocator,
 {
-    const FOREIGN_ALIGN: usize = core::mem::align_of::<T>();
+    const FOREIGN_ALIGN: usize = if core::mem::align_of::<T>() < A::MIN_ALIGN {
+        A::MIN_ALIGN
+    } else {
+        core::mem::align_of::<T>()
+    };
+
     type Borrowed<'a> = &'a T;
     type BorrowedMut<'a> = &'a mut T;
 
@@ -435,12 +440,12 @@ where
 }
 
 // SAFETY: The pointer returned by `into_foreign` comes from a well aligned
-// pointer to `T`.
+// pointer to `T` allocated by `A`.
 unsafe impl<T: 'static, A> ForeignOwnable for Pin<Box<T, A>>
 where
     A: Allocator,
 {
-    const FOREIGN_ALIGN: usize = core::mem::align_of::<T>();
+    const FOREIGN_ALIGN: usize = <Box<T, A> as ForeignOwnable>::FOREIGN_ALIGN;
     type Borrowed<'a> = Pin<&'a T>;
     type BorrowedMut<'a> = Pin<&'a mut T>;
 
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 63a66761d0c7..74121cf935f3 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -373,10 +373,10 @@ impl<T: ?Sized> Arc<T> {
     }
 }
 
-// SAFETY: The pointer returned by `into_foreign` comes from a well aligned
-// pointer to `ArcInner<T>`.
+// SAFETY: The pointer returned by `into_foreign` was originally allocated as an
+// `KBox<ArcInner<T>>`, so that type is what determines the alignment.
 unsafe impl<T: 'static> ForeignOwnable for Arc<T> {
-    const FOREIGN_ALIGN: usize = core::mem::align_of::<ArcInner<T>>();
+    const FOREIGN_ALIGN: usize = <KBox<ArcInner<T>> as ForeignOwnable>::FOREIGN_ALIGN;
 
     type Borrowed<'a> = ArcBorrow<'a, T>;
     type BorrowedMut<'a> = Self::Borrowed<'a>;