diff --git a/compiler/gen_llvm/src/llvm/bitcode.rs b/compiler/gen_llvm/src/llvm/bitcode.rs
index 713ef042c8..6db5633286 100644
--- a/compiler/gen_llvm/src/llvm/bitcode.rs
+++ b/compiler/gen_llvm/src/llvm/bitcode.rs
@@ -9,14 +9,17 @@ use crate::llvm::refcounting::{
     decrement_refcount_layout, increment_n_refcount_layout, increment_refcount_layout,
 };
 use inkwell::attributes::{Attribute, AttributeLoc};
-use inkwell::types::{BasicType, BasicTypeEnum};
+use inkwell::context::Context;
+use inkwell::types::{AnyType, BasicType, BasicTypeEnum};
 use inkwell::values::{BasicValue, BasicValueEnum, CallSiteValue, FunctionValue, InstructionValue};
 use inkwell::AddressSpace;
+use roc_builtins::bitcode;
 use roc_error_macros::internal_error;
 use roc_module::symbol::Symbol;
 use roc_mono::layout::{LambdaSet, Layout, LayoutIds, UnionLayout};
 
 use super::build::create_entry_block_alloca;
+use super::convert::zig_str_type;
 
 use std::convert::TryInto;
 
@@ -98,6 +101,21 @@ pub fn call_void_bitcode_fn<'a, 'ctx, 'env>(
         .unwrap_or_else(|| panic!("LLVM error: Tried to call void bitcode function, but got return value from bitcode function, {:?}", fn_name))
 }
 
+fn type_attribute<'ctx>(
+    context: &Context,
+    name: &str,
+    basic_type: BasicTypeEnum<'ctx>,
+) -> inkwell::attributes::Attribute {
+    let kind_id = Attribute::get_named_enum_kind_id(name);
+    context.create_type_attribute(kind_id, basic_type.as_any_type_enum())
+}
+
+fn enum_attribute<'ctx>(context: &Context, name: &str) -> inkwell::attributes::Attribute {
+    let kind_id = Attribute::get_named_enum_kind_id(name);
+    debug_assert!(kind_id > 0);
+    context.create_enum_attribute(kind_id, 1)
+}
+
 fn call_bitcode_fn_help<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     args: &[BasicValueEnum<'ctx>],
@@ -113,6 +131,34 @@ fn call_bitcode_fn_help<'a, 'ctx, 'env>(
 
     let call = env.builder.build_call(fn_val, &arguments, "call_builtin");
 
+    match fn_name {
+        bitcode::STR_NUMBER_OF_BYTES | bitcode::STR_COUNT_GRAPEHEME_CLUSTERS => {
+            // hacks
+
+            let i = 0;
+            call.add_attribute(
+                AttributeLoc::Param(0),
+                type_attribute(env.context, "byval", zig_str_type(env).into()),
+            );
+
+            call.add_attribute(
+                AttributeLoc::Param(i as u32),
+                enum_attribute(env.context, "nonnull"),
+            );
+
+            call.add_attribute(
+                AttributeLoc::Param(i as u32),
+                enum_attribute(env.context, "nocapture"),
+            );
+
+            call.add_attribute(
+                AttributeLoc::Param(i as u32),
+                enum_attribute(env.context, "readonly"),
+            );
+        }
+        _ => {}
+    }
+
     call.set_call_convention(fn_val.get_call_conventions());
     call
 }