diff --git a/nac3core/src/codegen/model/ptr.rs b/nac3core/src/codegen/model/ptr.rs
index 1721c0a4..740696de 100644
--- a/nac3core/src/codegen/model/ptr.rs
+++ b/nac3core/src/codegen/model/ptr.rs
@@ -114,9 +114,9 @@ impl<'ctx, Item: Model<'ctx>> Instance<'ctx, Ptr<Item>> {
     pub fn offset_const(
         &self,
         ctx: &CodeGenContext<'ctx, '_>,
-        offset: u64,
+        offset: i64,
     ) -> Instance<'ctx, Ptr<Item>> {
-        let offset = ctx.ctx.i32_type().const_int(offset, false);
+        let offset = ctx.ctx.i32_type().const_int(offset as u64, true);
         self.offset(ctx, offset)
     }
 
@@ -132,7 +132,7 @@ impl<'ctx, Item: Model<'ctx>> Instance<'ctx, Ptr<Item>> {
     pub fn set_index_const(
         &self,
         ctx: &CodeGenContext<'ctx, '_>,
-        index: u64,
+        index: i64,
         value: Instance<'ctx, Item>,
     ) {
         self.offset_const(ctx, index).store(ctx, value);
@@ -151,7 +151,7 @@ impl<'ctx, Item: Model<'ctx>> Instance<'ctx, Ptr<Item>> {
         &self,
         generator: &mut G,
         ctx: &CodeGenContext<'ctx, '_>,
-        index: u64,
+        index: i64,
     ) -> Instance<'ctx, Item> {
         self.offset_const(ctx, index).load(generator, ctx)
     }