diff --git a/fearless_simd_tests/Cargo.toml b/fearless_simd_tests/Cargo.toml
index 9eddb65d..16fcf8f8 100644
--- a/fearless_simd_tests/Cargo.toml
+++ b/fearless_simd_tests/Cargo.toml
@@ -9,6 +9,8 @@ description = "Safer and easier SIMD"
 readme = "README.md"
 rust-version.workspace = true
 publish = false
+# Tests are collected through tests/mod.rs; files beside it are modules, not separate integration crates.
+autotests = false
 
 [[test]]
 name = "tests"
diff --git a/fearless_simd_tests/tests/mod.rs b/fearless_simd_tests/tests/mod.rs
index 24c76c09..4d2f053d 100644
--- a/fearless_simd_tests/tests/mod.rs
+++ b/fearless_simd_tests/tests/mod.rs
@@ -10,6 +10,7 @@ use fearless_simd::*;
 use fearless_simd_dev_macros::simd_test;
 
 mod harness;
+mod soundness;
 
 // Ensure that we can cast between generic native-width vectors
 #[expect(dead_code, reason = "Compile only test")]
diff --git a/fearless_simd_tests/tests/soundness.rs b/fearless_simd_tests/tests/soundness.rs
new file mode 100644
index 00000000..04cd04c1
--- /dev/null
+++ b/fearless_simd_tests/tests/soundness.rs
@@ -0,0 +1,93 @@
+// Copyright 2026 the Fearless_SIMD Authors
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+#[cfg(panic = "unwind")]
+use std::panic::{AssertUnwindSafe, catch_unwind};
+
+use fearless_simd::*;
+use fearless_simd_dev_macros::simd_test;
+
+#[track_caller]
+#[cfg(panic = "unwind")]
+fn assert_panics(label: &str, f: impl FnOnce()) {
+    assert!(
+        catch_unwind(AssertUnwindSafe(f)).is_err(),
+        "{label} should panic"
+    );
+}
+
+#[cfg(not(panic = "unwind"))]
+fn assert_panics(_label: &str, _f: impl FnOnce()) {
+    // These tests need panic unwinding to observe rejected operations. Some targets, such as
+    // wasm32-wasip1, abort on panic instead.
+}
+
+macro_rules! for_each_simd_type {
+    ($test:ident, $simd:expr) => {
+        $test!($simd, f32x4, 4);
+        $test!($simd, i8x16, 16);
+        $test!($simd, u8x16, 16);
+        $test!($simd, mask8x16, 16);
+        $test!($simd, i16x8, 8);
+        $test!($simd, u16x8, 8);
+        $test!($simd, mask16x8, 8);
+        $test!($simd, i32x4, 4);
+        $test!($simd, u32x4, 4);
+        $test!($simd, mask32x4, 4);
+        $test!($simd, f64x2, 2);
+        $test!($simd, mask64x2, 2);
+        $test!($simd, f32x8, 8);
+        $test!($simd, i8x32, 32);
+        $test!($simd, u8x32, 32);
+        $test!($simd, mask8x32, 32);
+        $test!($simd, i16x16, 16);
+        $test!($simd, u16x16, 16);
+        $test!($simd, mask16x16, 16);
+        $test!($simd, i32x8, 8);
+        $test!($simd, u32x8, 8);
+        $test!($simd, mask32x8, 8);
+        $test!($simd, f64x4, 4);
+        $test!($simd, mask64x4, 4);
+        $test!($simd, f32x16, 16);
+        $test!($simd, i8x64, 64);
+        $test!($simd, u8x64, 64);
+        $test!($simd, mask8x64, 64);
+        $test!($simd, i16x32, 32);
+        $test!($simd, u16x32, 32);
+        $test!($simd, mask16x32, 32);
+        $test!($simd, i32x16, 16);
+        $test!($simd, u32x16, 16);
+        $test!($simd, mask32x16, 16);
+        $test!($simd, f64x8, 8);
+        $test!($simd, mask64x8, 8);
+    };
+}
+
+macro_rules! check_from_slice_short {
+    ($simd:expr, $vec:ident, $len:expr) => {
+        assert_panics(stringify!($vec::from_slice), || {
+            let _ = $vec::from_slice($simd, &[Default::default(); $len - 1]);
+        });
+    };
+}
+
+macro_rules! check_store_slice_short {
+    ($simd:expr, $vec:ident, $len:expr) => {{
+        let vec = $vec::from_slice($simd, &[Default::default(); $len]);
+        let mut short = [Default::default(); $len - 1];
+
+        assert_panics(stringify!($vec::store_slice), || {
+            vec.store_slice(&mut short)
+        });
+    }};
+}
+
+#[simd_test]
+fn from_slice_rejects_short_slice<S: Simd>(simd: S) {
+    for_each_simd_type!(check_from_slice_short, simd);
+}
+
+#[simd_test]
+fn store_slice_rejects_short_slice<S: Simd>(simd: S) {
+    for_each_simd_type!(check_store_slice_short, simd);
+}