diff --git a/src/machine.cpp b/src/machine.cpp
index 6ae39f7b30..24fd6c0a8e 100644
--- a/src/machine.cpp
+++ b/src/machine.cpp
@@ -273,6 +273,8 @@ killZombies(Thread* t, Thread* o)
 unsigned
 footprint(Thread* t)
 {
+  expect(t, t->criticalLevel == 0);
+
   unsigned n = t->heapOffset + t->heapIndex + t->backupHeapIndex;
 
   for (Thread* c = t->child; c; c = c->peer) {
@@ -592,6 +594,8 @@ postVisit(Thread* t, Heap::Visitor* v)
     m->tenuredWeakReferences = firstNewTenuredWeakReference;
   }
 
+  m->heap->postVisit();
+
   for (Reference* r = m->jniReferences; r; r = r->next) {
     if (r->weak) {
       if (m->heap->status(r->target) == Heap::Unreachable) {
@@ -2693,8 +2697,6 @@ class HeapClient: public Heap::Client {
   virtual void visitRoots(Heap::Visitor* v) {
     ::visitRoots(m, v);
 
-    m->heap->postVisit();
-
     postVisit(m->rootThread, v);
   }