diff --git a/reid-llvm-lib/examples/libtest.rs b/reid-llvm-lib/examples/libtest.rs
index 834a8fe..f33f871 100644
--- a/reid-llvm-lib/examples/libtest.rs
+++ b/reid-llvm-lib/examples/libtest.rs
@@ -1,4 +1,4 @@
-use reid_lib::{ConstValue, Context, Instr, CmpPredicate, TerminatorKind, Type};
+use reid_lib::{CmpPredicate, ConstValue, Context, FunctionFlags, Instr, TerminatorKind, Type};
 
 fn main() {
     use ConstValue::*;
@@ -8,10 +8,15 @@ fn main() {
 
     let mut module = context.module("test");
 
-    let main = module.function("main", Type::I32, Vec::new());
+    let main = module.function("main", Type::I32, Vec::new(), FunctionFlags::default());
     let mut m_entry = main.block("entry");
 
-    let fibonacci = module.function("fibonacci", Type::I32, vec![Type::I32]);
+    let fibonacci = module.function(
+        "fibonacci",
+        Type::I32,
+        vec![Type::I32],
+        FunctionFlags::default(),
+    );
 
     let arg = m_entry.build(Constant(I32(5))).unwrap();
     let fibonacci_call = m_entry
diff --git a/reid-llvm-lib/src/lib.rs b/reid-llvm-lib/src/lib.rs
index eba2147..819f93b 100644
--- a/reid-llvm-lib/src/lib.rs
+++ b/reid-llvm-lib/src/lib.rs
@@ -49,7 +49,13 @@ pub struct Module<'ctx> {
 }
 
 impl<'ctx> Module<'ctx> {
-    pub fn function(&mut self, name: &str, ret: Type, params: Vec<Type>) -> Function<'ctx> {
+    pub fn function(
+        &mut self,
+        name: &str,
+        ret: Type,
+        params: Vec<Type>,
+        flags: FunctionFlags,
+    ) -> Function<'ctx> {
         unsafe {
             Function {
                 phantom: PhantomData,
@@ -60,6 +66,7 @@ impl<'ctx> Module<'ctx> {
                         name: name.to_owned(),
                         ret,
                         params,
+                        flags,
                     },
                 ),
             }
@@ -76,6 +83,18 @@ pub struct FunctionData {
     name: String,
     ret: Type,
     params: Vec<Type>,
+    flags: FunctionFlags,
+}
+
+#[derive(Debug, Clone, Copy, Hash)]
+pub struct FunctionFlags {
+    pub is_extern: bool,
+}
+
+impl Default for FunctionFlags {
+    fn default() -> FunctionFlags {
+        FunctionFlags { is_extern: false }
+    }
 }
 
 pub struct Function<'ctx> {
diff --git a/reid/src/codegen.rs b/reid/src/codegen.rs
index 8b02f81..53eb947 100644
--- a/reid/src/codegen.rs
+++ b/reid/src/codegen.rs
@@ -1,8 +1,8 @@
 use std::{collections::HashMap, mem};
 
 use reid_lib::{
-    builder::InstructionValue, Block, CmpPredicate, ConstValue, Context, Function, Instr, Module,
-    TerminatorKind as Term, Type,
+    builder::InstructionValue, Block, CmpPredicate, ConstValue, Context, Function, FunctionFlags,
+    Instr, Module, TerminatorKind as Term, Type,
 };
 
 use crate::mir::{self, types::ReturnType, IndexedVariableReference, NamedVariableRef, TypeKind};
@@ -60,10 +60,21 @@ impl mir::Module {
                 .collect();
 
             let func = match &function.kind {
-                mir::FunctionDefinitionKind::Local(_, _) => {
-                    module.function(&function.name, function.return_type.get_type(), param_types)
-                }
-                mir::FunctionDefinitionKind::Extern => todo!(),
+                mir::FunctionDefinitionKind::Local(_, _) => module.function(
+                    &function.name,
+                    function.return_type.get_type(),
+                    param_types,
+                    FunctionFlags::default(),
+                ),
+                mir::FunctionDefinitionKind::Extern => module.function(
+                    &function.name,
+                    function.return_type.get_type(),
+                    param_types,
+                    FunctionFlags {
+                        is_extern: true,
+                        ..FunctionFlags::default()
+                    },
+                ),
             };
             functions.insert(function.name.clone(), func);
         }
diff --git a/reid/src/mir/typecheck.rs b/reid/src/mir/typecheck.rs
index 68a2a98..f3c782f 100644
--- a/reid/src/mir/typecheck.rs
+++ b/reid/src/mir/typecheck.rs
@@ -536,7 +536,7 @@ impl Literal {
                 (L::U64(_), TypeKind::U64) => self,
                 (L::U128(_), TypeKind::U128) => self,
                 (L::Bool(_), TypeKind::Bool) => self,
-                (L::String(val), TypeKind::StringPtr) => self,
+                (L::String(_), TypeKind::StringPtr) => self,
                 // TODO make sure that v is actually able to fit in the
                 // requested type
                 (L::Vague(VagueL::Number(v)), TypeKind::I8) => L::I8(v as i8),