diff --git a/compiler/builtins/bitcode/src/str.zig b/compiler/builtins/bitcode/src/str.zig
index 2172e693d7..801550663c 100644
--- a/compiler/builtins/bitcode/src/str.zig
+++ b/compiler/builtins/bitcode/src/str.zig
@@ -1150,8 +1150,8 @@ fn strToBytes(arg: RocStr) RocList {
 }
 
 const FromUtf8Result = extern struct {
-    byte_index: usize,
     string: RocStr,
+    byte_index: usize,
     is_ok: bool,
     problem_code: Utf8ByteProblem,
 };
diff --git a/compiler/gen_llvm/src/llvm/build_str.rs b/compiler/gen_llvm/src/llvm/build_str.rs
index 3b35d6d9a9..d143d06da6 100644
--- a/compiler/gen_llvm/src/llvm/build_str.rs
+++ b/compiler/gen_llvm/src/llvm/build_str.rs
@@ -295,8 +295,8 @@ pub fn str_from_utf8_range<'a, 'ctx, 'env>(
 
     let record_type = env.context.struct_type(
         &[
-            env.ptr_int().into(),
             super::convert::zig_str_type(env).into(),
+            env.ptr_int().into(),
             env.context.bool_type().into(),
             ctx.i8_type().into(),
         ],
@@ -343,8 +343,8 @@ pub fn str_from_utf8<'a, 'ctx, 'env>(
 
     let record_type = env.context.struct_type(
         &[
-            env.ptr_int().into(),
             super::convert::zig_str_type(env).into(),
+            env.ptr_int().into(),
             env.context.bool_type().into(),
             ctx.i8_type().into(),
         ],
diff --git a/compiler/mono/src/layout.rs b/compiler/mono/src/layout.rs
index 21d50f2715..0afcae5d15 100644
--- a/compiler/mono/src/layout.rs
+++ b/compiler/mono/src/layout.rs
@@ -1151,10 +1151,13 @@ impl<'a> Builtin<'a> {
             Float64 => align_of::<f64>() as u32,
             Float32 => align_of::<f32>() as u32,
             Float16 => align_of::<i16>() as u32,
-            Str | EmptyStr => pointer_size,
             Dict(_, _) | EmptyDict => pointer_size,
             Set(_) | EmptySet => pointer_size,
-            List(_) | EmptyList => pointer_size,
+            // we often treat these as i128 (64-bit systems)
+            // or i64 (32-bit systems). For that to be safe
+            // they must be aligned to allow such access
+            List(_) | EmptyList => 2 * pointer_size,
+            Str | EmptyStr => 2 * pointer_size,
         }
     }
 
@@ -1240,9 +1243,10 @@ impl<'a> Builtin<'a> {
             Builtin::Str => pointer_size,
             Builtin::Dict(k, v) => k
                 .alignment_bytes(pointer_size)
-                .max(v.alignment_bytes(pointer_size)),
-            Builtin::Set(k) => k.alignment_bytes(pointer_size),
-            Builtin::List(e) => e.alignment_bytes(pointer_size),
+                .max(v.alignment_bytes(pointer_size))
+                .max(pointer_size),
+            Builtin::Set(k) => k.alignment_bytes(pointer_size).max(pointer_size),
+            Builtin::List(e) => e.alignment_bytes(pointer_size).max(pointer_size),
             Builtin::EmptyStr | Builtin::EmptyList | Builtin::EmptyDict | Builtin::EmptySet => {
                 unreachable!("not heap-allocated")
             }