diff --git a/src/ast/vm.rs b/src/ast/vm.rs
index 30e0f93..249d82d 100644
--- a/src/ast/vm.rs
+++ b/src/ast/vm.rs
@@ -168,6 +168,13 @@ impl VM {
                         } else {
                             self.unpack(&closure.parameter_node, &next_args, &mut 0)?;
                         }
+
+                        // PRE-ALLOCATION
+                        let current_stack = self.stack.len() as u32;
+                        if closure.stack_size > current_stack {
+                            self.stack.resize(closure.stack_size as usize, Value::Void);
+                        }
+
                         result = self.eval_observed(observer, &closure.exec_node);
                         self.frames.pop();
                     } else if let Some(series) = next_obj.as_series() {
@@ -239,9 +246,7 @@ impl VM {
         // Fill remaining stack slots with Void
         let current_stack = self.stack.len() as u32;
         if closure.stack_size > current_stack {
-            for _ in 0..(closure.stack_size - current_stack) {
-                self.stack.push(Value::Void);
-            }
+            self.stack.resize(closure.stack_size as usize, Value::Void);
         }
 
         self.frames.push(CallFrame {
@@ -263,9 +268,7 @@ impl VM {
         self.stack.clear();
         self.frames.clear();
 
-        for _ in 0..stack_size {
-            self.stack.push(Value::Void);
-        }
+        self.stack.resize(stack_size as usize, Value::Void);
 
         self.frames.push(CallFrame {
             stack_base: 0,
@@ -697,7 +700,14 @@ impl VM {
                                 };
 
                                 let res = match unpack_res {
-                                    Ok(_) => self.eval_internal(obs, &closure.exec_node),
+                                    Ok(_) => {
+                                        // PRE-ALLOCATION
+                                        let current_stack = (self.stack.len() - base) as u32;
+                                        if closure.stack_size > current_stack {
+                                            self.stack.resize(base + closure.stack_size as usize, Value::Void);
+                                        }
+                                        self.eval_internal(obs, &closure.exec_node)
+                                    }
                                     Err(e) => Err(e),
                                 };