diff --git a/crates/core_simd/src/round.rs b/crates/core_simd/src/round.rs
index d77bc4e8fa7..ee232e2b222 100644
--- a/crates/core_simd/src/round.rs
+++ b/crates/core_simd/src/round.rs
@@ -2,7 +2,10 @@ macro_rules! implement {
     {
         $type:ident, $int_type:ident
     } => {
-        impl<const LANES: usize> crate::$type<LANES> {
+        impl<const LANES: usize> crate::$type<LANES>
+        where
+            Self: crate::LanesAtMost64,
+        {
             /// Returns the largest integer less than or equal to each lane.
             #[must_use = "method returns a new vector and does not mutate the original value"]
             #[inline]
@@ -16,7 +19,13 @@ macro_rules! implement {
             pub fn ceil(self) -> Self {
                 unsafe { crate::intrinsics::simd_ceil(self) }
             }
+        }
 
+        impl<const LANES: usize> crate::$type<LANES>
+        where
+            Self: crate::LanesAtMost64,
+            crate::$int_type<LANES>: crate::LanesAtMost64,
+        {
             /// Rounds toward zero and converts to the same-width integer type, assuming that
             /// the value is finite and fits in that type.
             ///
diff --git a/crates/core_simd/src/vectors_f32.rs b/crates/core_simd/src/vectors_f32.rs
index 0b5d8c6ec49..5bb8f3a1c34 100644
--- a/crates/core_simd/src/vectors_f32.rs
+++ b/crates/core_simd/src/vectors_f32.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `f32` values.
 #[repr(simd)]
-pub struct SimdF32<const LANES: usize>([f32; LANES]);
+pub struct SimdF32<const LANES: usize>([f32; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_float_vector! { SimdF32, f32, SimdU32 }
 
diff --git a/crates/core_simd/src/vectors_f64.rs b/crates/core_simd/src/vectors_f64.rs
index 307f8a4acac..c0dca6a52ac 100644
--- a/crates/core_simd/src/vectors_f64.rs
+++ b/crates/core_simd/src/vectors_f64.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `f64` values.
 #[repr(simd)]
-pub struct SimdF64<const LANES: usize>([f64; LANES]);
+pub struct SimdF64<const LANES: usize>([f64; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_float_vector! { SimdF64, f64, SimdU64 }
 
diff --git a/crates/core_simd/src/vectors_i128.rs b/crates/core_simd/src/vectors_i128.rs
index 16e6162be55..568fa81da80 100644
--- a/crates/core_simd/src/vectors_i128.rs
+++ b/crates/core_simd/src/vectors_i128.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `i128` values.
 #[repr(simd)]
-pub struct SimdI128<const LANES: usize>([i128; LANES]);
+pub struct SimdI128<const LANES: usize>([i128; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_integer_vector! { SimdI128, i128 }
 
diff --git a/crates/core_simd/src/vectors_i16.rs b/crates/core_simd/src/vectors_i16.rs
index 08cc4af2a5e..d77e593a2ed 100644
--- a/crates/core_simd/src/vectors_i16.rs
+++ b/crates/core_simd/src/vectors_i16.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `i16` values.
 #[repr(simd)]
-pub struct SimdI16<const LANES: usize>([i16; LANES]);
+pub struct SimdI16<const LANES: usize>([i16; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_integer_vector! { SimdI16, i16 }
 
diff --git a/crates/core_simd/src/vectors_i32.rs b/crates/core_simd/src/vectors_i32.rs
index 116f2abaeee..0a89eeda3b2 100644
--- a/crates/core_simd/src/vectors_i32.rs
+++ b/crates/core_simd/src/vectors_i32.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `i32` values.
 #[repr(simd)]
-pub struct SimdI32<const LANES: usize>([i32; LANES]);
+pub struct SimdI32<const LANES: usize>([i32; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_integer_vector! { SimdI32, i32 }
 
diff --git a/crates/core_simd/src/vectors_i64.rs b/crates/core_simd/src/vectors_i64.rs
index 6a1e2094179..017140654a5 100644
--- a/crates/core_simd/src/vectors_i64.rs
+++ b/crates/core_simd/src/vectors_i64.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `i64` values.
 #[repr(simd)]
-pub struct SimdI64<const LANES: usize>([i64; LANES]);
+pub struct SimdI64<const LANES: usize>([i64; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_integer_vector! { SimdI64, i64 }
 
diff --git a/crates/core_simd/src/vectors_i8.rs b/crates/core_simd/src/vectors_i8.rs
index 0ac5ba9efee..e21126533b8 100644
--- a/crates/core_simd/src/vectors_i8.rs
+++ b/crates/core_simd/src/vectors_i8.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `i8` values.
 #[repr(simd)]
-pub struct SimdI8<const LANES: usize>([i8; LANES]);
+pub struct SimdI8<const LANES: usize>([i8; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_integer_vector! { SimdI8, i8 }
 
diff --git a/crates/core_simd/src/vectors_isize.rs b/crates/core_simd/src/vectors_isize.rs
index 6856f305092..ee23dfe7d86 100644
--- a/crates/core_simd/src/vectors_isize.rs
+++ b/crates/core_simd/src/vectors_isize.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `isize` values.
 #[repr(simd)]
-pub struct SimdIsize<const LANES: usize>([isize; LANES]);
+pub struct SimdIsize<const LANES: usize>([isize; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_integer_vector! { SimdIsize, isize }
 
diff --git a/crates/core_simd/src/vectors_u128.rs b/crates/core_simd/src/vectors_u128.rs
index 522404f133e..7931b9e088f 100644
--- a/crates/core_simd/src/vectors_u128.rs
+++ b/crates/core_simd/src/vectors_u128.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `u128` values.
 #[repr(simd)]
-pub struct SimdU128<const LANES: usize>([u128; LANES]);
+pub struct SimdU128<const LANES: usize>([u128; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_integer_vector! { SimdU128, u128 }
 
diff --git a/crates/core_simd/src/vectors_u16.rs b/crates/core_simd/src/vectors_u16.rs
index efe7dea58dc..91c0e616808 100644
--- a/crates/core_simd/src/vectors_u16.rs
+++ b/crates/core_simd/src/vectors_u16.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `u16` values.
 #[repr(simd)]
-pub struct SimdU16<const LANES: usize>([u16; LANES]);
+pub struct SimdU16<const LANES: usize>([u16; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_integer_vector! { SimdU16, u16 }
 
diff --git a/crates/core_simd/src/vectors_u32.rs b/crates/core_simd/src/vectors_u32.rs
index a6cef5baeb7..b0400b5ba3a 100644
--- a/crates/core_simd/src/vectors_u32.rs
+++ b/crates/core_simd/src/vectors_u32.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `u32` values.
 #[repr(simd)]
-pub struct SimdU32<const LANES: usize>([u32; LANES]);
+pub struct SimdU32<const LANES: usize>([u32; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_integer_vector! { SimdU32, u32 }
 
diff --git a/crates/core_simd/src/vectors_u64.rs b/crates/core_simd/src/vectors_u64.rs
index 3982e30f570..0f3712241fe 100644
--- a/crates/core_simd/src/vectors_u64.rs
+++ b/crates/core_simd/src/vectors_u64.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `u64` values.
 #[repr(simd)]
-pub struct SimdU64<const LANES: usize>([u64; LANES]);
+pub struct SimdU64<const LANES: usize>([u64; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_integer_vector! { SimdU64, u64 }
 
diff --git a/crates/core_simd/src/vectors_usize.rs b/crates/core_simd/src/vectors_usize.rs
index c882898f9fb..ea089aeb9d3 100644
--- a/crates/core_simd/src/vectors_usize.rs
+++ b/crates/core_simd/src/vectors_usize.rs
@@ -2,7 +2,9 @@
 
 /// A SIMD vector of containing `LANES` `usize` values.
 #[repr(simd)]
-pub struct SimdUsize<const LANES: usize>([usize; LANES]);
+pub struct SimdUsize<const LANES: usize>([usize; LANES])
+where
+    Self: crate::LanesAtMost64;
 
 impl_integer_vector! { SimdUsize, usize }