diff --git a/crates/compiler/gen_llvm/src/llvm/lowlevel.rs b/crates/compiler/gen_llvm/src/llvm/lowlevel.rs
index b768b1d7fe..48e63b6330 100644
--- a/crates/compiler/gen_llvm/src/llvm/lowlevel.rs
+++ b/crates/compiler/gen_llvm/src/llvm/lowlevel.rs
@@ -849,13 +849,22 @@ pub(crate) fn run_low_level<'a, 'ctx>(
             // List.concatUtf8: List U8, Str -> List U8
             arguments!(list, string);
 
-            call_list_bitcode_fn(
-                env,
-                &[list.into_struct_value()],
-                &[string],
-                BitcodeReturns::List,
-                bitcode::LIST_CONCAT_UTF8,
-            )
+            match env.target.ptr_width() {
+                PtrWidth::Bytes4 => call_str_bitcode_fn(
+                    env,
+                    &[list, string],
+                    &[],
+                    BitcodeReturns::List,
+                    bitcode::LIST_CONCAT_UTF8,
+                ),
+                PtrWidth::Bytes8 => call_list_bitcode_fn(
+                    env,
+                    &[list.into_struct_value()],
+                    &[string],
+                    BitcodeReturns::List,
+                    bitcode::LIST_CONCAT_UTF8,
+                ),
+            }
         }
         NumToStr => {
             // Num.toStr : Num a -> Str