diff --git a/src/bytecode.rs b/src/bytecode.rs
index 6ee9227..90b45db 100644
--- a/src/bytecode.rs
+++ b/src/bytecode.rs
@@ -38,7 +38,7 @@ pub enum OpCode {
     JmpIfFalse { step: usize },
 
     /// push an empty attribute set onto stack
-    AttrSet,
+    AttrSet { cap: usize },
     /// finalize the recursive attribute set at TOS
     FinalizeRec,
     /// [ .. set value ] consume 1 element, push a static kv pair (`name`, `value`) into `set`
diff --git a/src/compile.rs b/src/compile.rs
index 1000701..5b41b0f 100644
--- a/src/compile.rs
+++ b/src/compile.rs
@@ -97,7 +97,7 @@ impl Compile for ir::Thunk {
 
 impl Compile for ir::Attrs {
     fn compile(self, comp: &mut Compiler) {
-        comp.push(OpCode::AttrSet);
+        comp.push(OpCode::AttrSet { cap: self.stcs.len() + self.dyns.len() });
         for stc in self.stcs {
             stc.1.compile(comp);
             if !self.rec {
@@ -250,17 +250,17 @@ impl Compile for ir::HasAttr {
         for attr in self.rhs {
             match attr {
                 ir::Attr::Str(sym) => {
-                    comp.push(OpCode::AttrSet);
+                    comp.push(OpCode::AttrSet { cap: 0 });
                     comp.push(OpCode::SelectOrDefault { sym })
                 }
                 ir::Attr::Dynamic(dynamic) => {
                     dynamic.compile(comp);
-                    comp.push(OpCode::AttrSet);
+                    comp.push(OpCode::AttrSet { cap: 0 });
                     comp.push(OpCode::SelectDynamicOrDefault);
                 }
                 ir::Attr::Strs(string) => {
                     string.compile(comp);
-                    comp.push(OpCode::AttrSet);
+                    comp.push(OpCode::AttrSet { cap: 0 });
                     comp.push(OpCode::SelectDynamicOrDefault);
                 }
             }
@@ -281,17 +281,17 @@ impl Compile for ir::Select {
         for attr in self.attrpath {
             match attr {
                 ir::Attr::Str(sym) => {
-                    comp.push(OpCode::AttrSet);
+                    comp.push(OpCode::AttrSet { cap: 0 });
                     comp.push(OpCode::SelectOrDefault { sym })
                 }
                 ir::Attr::Dynamic(dynamic) => {
                     dynamic.compile(comp);
-                    comp.push(OpCode::AttrSet);
+                    comp.push(OpCode::AttrSet { cap: 0 });
                     comp.push(OpCode::SelectDynamicOrDefault);
                 }
                 ir::Attr::Strs(string) => {
                     string.compile(comp);
-                    comp.push(OpCode::AttrSet);
+                    comp.push(OpCode::AttrSet { cap: 0 });
                     comp.push(OpCode::SelectDynamicOrDefault);
                 }
             }
diff --git a/src/ty/internal/attrset.rs b/src/ty/internal/attrset.rs
index 498f546..dca7d84 100644
--- a/src/ty/internal/attrset.rs
+++ b/src/ty/internal/attrset.rs
@@ -1,3 +1,5 @@
+use std::hash::Hash;
+
 use hashbrown::{HashMap, HashSet};
 
 use derive_more::Constructor;
@@ -22,6 +24,10 @@ impl<'vm> AttrSet<'vm> {
         }
     }
 
+    pub fn with_capacity(cap: usize) -> Self {
+        AttrSet { data: HashMap::with_capacity(cap) }
+    }
+
     pub fn push_attr_force(&mut self, sym: usize, val: Value<'vm>) {
         self.data.insert(sym, val);
     }
diff --git a/src/vm/mod.rs b/src/vm/mod.rs
index a18e2c8..70c8bfb 100644
--- a/src/vm/mod.rs
+++ b/src/vm/mod.rs
@@ -182,8 +182,8 @@ impl<'vm, 'jit: 'vm> VM<'jit> {
                 let elem = stack.pop();
                 stack.tos_mut()?.push(elem);
             }
-            OpCode::AttrSet => {
-                stack.push(Value::AttrSet(AttrSet::empty().into()))?;
+            OpCode::AttrSet { cap } => {
+                stack.push(Value::AttrSet(AttrSet::with_capacity(cap).into()))?;
             }
             OpCode::FinalizeRec => {
                 let env = env.clone().enter(