diff --git a/src/compile.rs b/src/compile.rs
index 69fcdb6..3cea605 100644
--- a/src/compile.rs
+++ b/src/compile.rs
@@ -25,15 +25,27 @@ impl State {
     }
 }
 
-#[derive(Clone, Debug, Default)]
+#[derive(Clone, Debug)]
 pub struct Scope {
     pub locals: HashMap<String, u16>,
     pub register_counter: LocalCounter,
-    pub highest_upvalue: u16,
+    pub highest_upvalue: i32,
     pub upvalues: HashMap<String, u16>,
     pub is_vararg: bool,
 }
 
+impl Default for Scope {
+    fn default() -> Self {
+        Self {
+            locals: Default::default(),
+            register_counter: Default::default(),
+            highest_upvalue: -1,
+            upvalues: Default::default(),
+            is_vararg: Default::default(),
+        }
+    }
+}
+
 #[derive(Clone, Debug, Default)]
 pub struct LocalCounter(u16, Vec<u16>);
 
@@ -866,11 +878,12 @@ impl Expression {
                     }
                 }
 
-                inner_scope.highest_upvalue = scope.highest_upvalue + scope.register_counter.0;
+                inner_scope.highest_upvalue =
+                    scope.highest_upvalue + scope.register_counter.0 as i32;
                 inner_scope.upvalues = scope.upvalues.clone();
 
                 for (name, reg) in &scope.locals {
-                    let new_reg = *reg + scope.highest_upvalue + 1;
+                    let new_reg = *reg + (scope.highest_upvalue + 1) as u16;
                     inner_scope.upvalues.insert(name.clone(), new_reg);
                 }
 
diff --git a/src/vm.rs b/src/vm.rs
index 3a87950..34b8fa3 100644
--- a/src/vm.rs
+++ b/src/vm.rs
@@ -661,13 +661,13 @@ impl ClosureRunner {
             .closure
             .upvalues
             .iter()
-            .map(|(v, _)| *v)
+            .map(|(v, _)| *v as i32)
             .max()
-            .unwrap_or(0);
+            .unwrap_or(-1);
 
         let mut upvalues = self.closure.upvalues.clone();
         for (reg, value) in &self.stack {
-            upvalues.insert(reg + highest_upvalue + 1, value.clone());
+            upvalues.insert(reg + (highest_upvalue + 1) as u16, value.clone());
         }
         upvalues
     }