diff --git a/crates/compiler/load_internal/src/file.rs b/crates/compiler/load_internal/src/file.rs
index 1c7c6dd6ed..a33d581d1b 100644
--- a/crates/compiler/load_internal/src/file.rs
+++ b/crates/compiler/load_internal/src/file.rs
@@ -4664,7 +4664,7 @@ fn synth_import(subs: &mut Subs, content: roc_types::subs::Content) -> Variable
 fn synth_list_len_type(subs: &mut Subs) -> Variable {
     use roc_types::subs::{Content, FlatType, LambdaSet, OptVariable, SubsSlice, UnionLabels};
 
-    // List.len : List a -> Nat
+    // List.len : List a -> U64
     let a = synth_import(subs, Content::FlexVar(None));
     let a_slice = SubsSlice::extend_new(&mut subs.variables, [a]);
     let list_a = synth_import(
@@ -4685,7 +4685,7 @@ fn synth_list_len_type(subs: &mut Subs) -> Variable {
     let fn_args_slice = SubsSlice::extend_new(&mut subs.variables, [list_a]);
     subs.set_content(
         fn_var,
-        Content::Structure(FlatType::Func(fn_args_slice, clos_list_len, Variable::NAT)),
+        Content::Structure(FlatType::Func(fn_args_slice, clos_list_len, Variable::U64)),
     );
     fn_var
 }