diff --git a/nac3core/src/codegen/model/structure.rs b/nac3core/src/codegen/model/structure.rs
index c158bd94..c91f42aa 100644
--- a/nac3core/src/codegen/model/structure.rs
+++ b/nac3core/src/codegen/model/structure.rs
@@ -31,7 +31,7 @@ pub trait FieldTraversal<'ctx> {
 #[derive(Debug, Clone, Copy)]
 pub struct GepField<M> {
     /// The GEP index of this field. This is the index to use with `build_gep`.
-    pub gep_index: u64,
+    pub gep_index: u32,
     /// The cosmetic name of this field.
     pub name: &'static str,
     /// The [`Model`] of this field's type.
@@ -41,7 +41,7 @@ pub struct GepField<M> {
 /// A traversal to calculate the GEP index of fields.
 pub struct GepFieldTraversal {
     /// The current GEP index.
-    gep_index_counter: u64,
+    gep_index_counter: u32,
 }
 
 impl<'ctx> FieldTraversal<'ctx> for GepFieldTraversal {
@@ -302,7 +302,7 @@ impl<'ctx, S: StructKind<'ctx>> Instance<'ctx, Struct<S>> {
         GetField: FnOnce(S::Fields<GepFieldTraversal>) -> GepField<M>,
     {
         let field = get_field(self.model.0.fields());
-        let val = self.value.get_field_at_index(field.gep_index as u32).unwrap();
+        let val = self.value.get_field_at_index(field.gep_index).unwrap();
         field.model.check_value(generator, ctx, val).unwrap()
     }
 }
@@ -325,7 +325,7 @@ impl<'ctx, S: StructKind<'ctx>> Instance<'ctx, Ptr<Struct<S>>> {
             ctx.builder
                 .build_in_bounds_gep(
                     self.value,
-                    &[llvm_i32.const_zero(), llvm_i32.const_int(field.gep_index, false)],
+                    &[llvm_i32.const_zero(), llvm_i32.const_int(u64::from(field.gep_index), false)],
                     field.name,
                 )
                 .unwrap()