diff --git a/.github/workflows/rust.yml b/.github/workflows/rust.yml
index a76522a..206d798 100644
--- a/.github/workflows/rust.yml
+++ b/.github/workflows/rust.yml
@@ -22,8 +22,11 @@ jobs:
           cargo miri setup
       - name: Test (default) with Miri
         run: MIRIFLAGS=-Zmiri-strict-provenance cargo miri test
+      - name: Test (default) with Miri + Tree Borrows
+        run: MIRIFLAGS="-Zmiri-strict-provenance -Zmiri-tree-borrows" cargo miri test
+      # AutoThinVec needs tree borrows.
       - name: Test (gecko-ffi) with Miri
-        run: MIRIFLAGS=-Zmiri-strict-provenance cargo miri test --features=gecko-ffi
+        run: MIRIFLAGS="-Zmiri-strict-provenance -Zmiri-tree-borrows" cargo miri test --features=gecko-ffi
       - name: Test (unstable features) with Miri
         run: MIRIFLAGS=-Zmiri-strict-provenance cargo miri test --features=unstable
 
diff --git a/src/lib.rs b/src/lib.rs
index f0630ac..5db06a2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2681,6 +2681,7 @@ impl<T, const N: usize> AutoThinVec<T, N> {
         debug_assert!(self.is_singleton());
         let this = unsafe { self.get_unchecked_mut() };
         this.buffer.header.set_len(0);
+        // TODO(emilio): Use NonNull::from_mut when msrv allows.
         this.inner.ptr = NonNull::new_unchecked(&mut this.buffer.header);
     }
 
@@ -2728,7 +2729,7 @@ impl<T, const N: usize> Deref for AutoThinVec<T, N> {
 #[macro_export]
 macro_rules! auto_thin_vec {
     (let $name:ident : [$ty:ty; $cap:literal]) => {
-        let mut auto_vec = $crate::AutoThinVec::<$ty, $cap>::new_unpinned();
+        let auto_vec = $crate::AutoThinVec::<$ty, $cap>::new_unpinned();
         let mut $name = core::pin::pin!(auto_vec);
         unsafe { $name.as_mut().shrink_to_fit_known_singleton() };
     };
@@ -4355,6 +4356,38 @@ mod std_tests {
         }
     */
 
+    #[cfg(all(feature = "gecko-ffi"))]
+    #[test]
+    fn auto_t_array_basic() {
+        crate::auto_thin_vec!(let t: [u8; 10]);
+        assert_eq!(t.capacity(), 10);
+        assert!(!t.has_allocation());
+        {
+            let inner = unsafe { &mut *t.as_mut().as_mut_ptr() };
+            for i in 0..30 {
+                inner.push(i as u8);
+            }
+        }
+
+        assert_eq!(t.len(), 30);
+        assert!(t.has_allocation());
+        assert_eq!(t[5], 5);
+        assert_eq!(t[29], 29);
+        assert!(t.capacity() >= 30);
+
+        {
+            let inner = unsafe { &mut *t.as_mut().as_mut_ptr() };
+            inner.truncate(5);
+        }
+
+        assert_eq!(t.len(), 5);
+        assert!(t.capacity() >= 30);
+        assert!(t.has_allocation());
+        t.as_mut().shrink_to_fit();
+        assert!(!t.has_allocation());
+        assert_eq!(t.capacity(), 10);
+    }
+
     #[test]
     #[cfg_attr(feature = "gecko-ffi", ignore)]
     fn test_header_data() {