diff --git a/src/run/net.rs b/src/run/net.rs
index 36a2e690..c4bb3a9b 100644
--- a/src/run/net.rs
+++ b/src/run/net.rs
@@ -23,11 +23,9 @@ impl<'h, M: Mode> Net<'h, M> {
     Net { linker: Linker::new(heap), tid: 0, tids: 1, trgs: vec![Trg::port(Port(0)); 1 << 16], root }
   }
 
-  /// Boots a net from a Ref.
+  /// Boots a net from a Def.
   pub fn boot(&mut self, def: &Def) {
-    let def = Port::new_ref(def);
-    trace!(self, def);
-    self.root.set_target(def);
+    self.call(Port::new_ref(def), self.root.as_var());
   }
 }
 
@@ -47,36 +45,6 @@ impl<'a, M: Mode> Net<'a, M> {
     count
   }
 
-  /// Expands [`Ref`] nodes in the tree connected to `root`.
-  #[inline(always)]
-  pub fn expand(&mut self) {
-    assert!(!M::LAZY);
-    fn go<M: Mode>(net: &mut Net<M>, wire: Wire, len: usize, key: usize) {
-      trace!(net.tracer, wire);
-      let port = wire.load_target();
-      trace!(net.tracer, port);
-      if port == Port::LOCK {
-        return;
-      }
-      if port.tag() == Ctr {
-        let node = port.traverse_node();
-        if len >= net.tids || key % 2 == 0 {
-          go(net, node.p1, len.saturating_mul(2), key / 2);
-        }
-        if len >= net.tids || key % 2 == 1 {
-          go(net, node.p2, len.saturating_mul(2), key / 2);
-        }
-      } else if port.tag() == Ref && port != Port::ERA {
-        let got = wire.swap_target(Port::LOCK);
-        if got != Port::LOCK {
-          trace!(net.tracer, port, wire);
-          net.call(port, Port::new_var(wire.addr()));
-        }
-      }
-    }
-    go(self, self.root.clone(), 1, self.tid);
-  }
-
   // Lazy mode weak head normalizer
   #[inline(always)]
   fn weak_normal(&mut self, mut prev: Port, root: Wire) -> Port {
@@ -146,7 +114,48 @@ impl<'a, M: Mode> Net<'a, M> {
       self.expand();
       while !self.redexes.is_empty() {
         self.reduce(usize::MAX);
-        self.expand();
+      }
+    }
+  }
+}
+
+impl<'h, M: Mode> Net<'h, M> {
+  /// Expands [`Tag::Ref`] nodes in the tree connected to `root`.
+  pub fn expand(&mut self) {
+    assert!(!M::LAZY);
+    let (new_root, out_port) = self.create_wire();
+    let old_root = std::mem::replace(&mut self.root, new_root);
+    self.link_wire_port(old_root, ExpandDef::new(out_port));
+  }
+}
+
+struct ExpandDef {
+  out: Port,
+}
+
+impl ExpandDef {
+  fn new(out: Port) -> Port {
+    Port::new_ref(Box::leak(Box::new(Def::new(LabSet::ALL, ExpandDef { out }))))
+  }
+}
+
+impl AsDef for ExpandDef {
+  unsafe fn call<M: Mode>(def: *const Def<Self>, net: &mut Net<M>, port: Port) {
+    if port.tag() == Tag::Ref && port != Port::ERA {
+      return net.call(port, Port::new_ref(Def::upcast(unsafe { &*def })));
+    }
+    let def = *Box::from_raw(def as *mut Def<Self>);
+    match port.tag() {
+      Tag::Red => {
+        unreachable!()
+      }
+      Tag::Ref | Tag::Num | Tag::Var => net.link_port_port(def.data.out, port),
+      tag @ (Tag::Op2 | Tag::Op1 | Tag::Mat | Tag::Ctr) => {
+        let old = port.consume_node();
+        let new = net.create_node(tag, old.lab);
+        net.link_port_port(def.data.out, new.p0);
+        net.link_wire_port(old.p1, ExpandDef::new(new.p1));
+        net.link_wire_port(old.p2, ExpandDef::new(new.p2));
       }
     }
   }
diff --git a/src/run/parallel.rs b/src/run/parallel.rs
index 9207a0eb..1fc97fde 100644
--- a/src/run/parallel.rs
+++ b/src/run/parallel.rs
@@ -24,6 +24,8 @@ impl<'h, M: Mode> Net<'h, M> {
   pub fn parallel_normal(&mut self) {
     assert!(!M::LAZY);
 
+    self.expand();
+
     const SHARE_LIMIT: usize = 1 << 12; // max share redexes per split
     const LOCAL_LIMIT: usize = 1 << 18; // max local rewrites per epoch
 
@@ -77,7 +79,6 @@ impl<'h, M: Mode> Net<'h, M> {
     fn main<M: Mode>(ctx: &mut ThreadContext<M>) {
       loop {
         reduce(ctx);
-        ctx.net.expand();
         if count(ctx) == 0 {
           break;
         }