diff --git a/crates/compiler/builtins/bitcode/src/str.zig b/crates/compiler/builtins/bitcode/src/str.zig
index a8732aa2e1..af101421fe 100644
--- a/crates/compiler/builtins/bitcode/src/str.zig
+++ b/crates/compiler/builtins/bitcode/src/str.zig
@@ -1552,7 +1552,7 @@ const CountAndStart = extern struct {
     start: usize,
 };
 
-pub fn fromUtf8C(arg: RocList, update_mode: UpdateMode, output: *FromUtf8Result) callconv(.C) void {
+pub fn fromUtf8C(output: *FromUtf8Result, arg: RocList, update_mode: UpdateMode) callconv(.C) void {
     output.* = fromUtf8(arg, update_mode);
 }
 
diff --git a/crates/compiler/gen_llvm/src/llvm/build_str.rs b/crates/compiler/gen_llvm/src/llvm/build_str.rs
index 12b24b2dea..ce246320fa 100644
--- a/crates/compiler/gen_llvm/src/llvm/build_str.rs
+++ b/crates/compiler/gen_llvm/src/llvm/build_str.rs
@@ -194,9 +194,9 @@ pub fn str_from_utf8<'a, 'ctx, 'env>(
     call_void_bitcode_fn(
         env,
         &[
+            result_ptr.into(),
             list_symbol_to_c_abi(env, scope, list).into(),
             pass_update_mode(env, update_mode),
-            result_ptr.into(),
         ],
         bitcode::STR_FROM_UTF8,
     );
diff --git a/crates/compiler/gen_wasm/src/low_level.rs b/crates/compiler/gen_wasm/src/low_level.rs
index cd2ee66f64..02d7a10346 100644
--- a/crates/compiler/gen_wasm/src/low_level.rs
+++ b/crates/compiler/gen_wasm/src/low_level.rs
@@ -265,29 +265,20 @@ impl<'a> LowLevelCall<'a> {
                 Low-level op returns a struct with all the data for both Ok and Err.
                 Roc AST wrapper converts this to a tag union, with app-dependent tag IDs.
 
-                fromUtf8C(arg: RocList, update_mode: UpdateMode, output: *FromUtf8Result) callconv(.C) void
+                fromUtf8C(output: *FromUtf8Result, arg: RocList, update_mode: UpdateMode) callconv(.C) void
+                    output: *FromUtf8Result   i32
                     arg: RocList              i64, i32
                     update_mode: UpdateMode   i32
-                    output: *FromUtf8Result   i32
                 */
-
-                let (ret_ptr, ret_offset) = match &self.ret_storage {
-                    StoredValue::StackMemory { location, .. } => {
-                        location.local_and_offset(backend.storage.stack_frame_pointer)
-                    }
-                    _ => internal_error!("Low-level op StrFromUtf8 should return a struct"),
-                };
-
-                // Return pointer is the last arg rather than the first, so we can't use the usual helper.
-                backend
-                    .storage
-                    .load_symbol_zig(&mut backend.code_builder, self.arguments[0]);
+                backend.storage.load_symbols_for_call(
+                    backend.env.arena,
+                    &mut backend.code_builder,
+                    self.arguments,
+                    self.ret_symbol,
+                    &WasmLayout::new(&self.ret_layout),
+                    CallConv::Zig,
+                );
                 backend.code_builder.i32_const(UPDATE_MODE_IMMUTABLE);
-                backend.code_builder.get_local(ret_ptr);
-                if ret_offset != 0 {
-                    backend.code_builder.i32_const(ret_offset as i32);
-                    backend.code_builder.i32_add();
-                }
                 backend.call_host_fn_after_loading_args(bitcode::STR_FROM_UTF8, 4, false);
             }
             StrTrimLeft => self.load_args_and_call_zig(backend, bitcode::STR_TRIM_LEFT),