diff --git a/src/heap.cpp b/src/heap.cpp
index f437955d35..8ec6820f71 100644
--- a/src/heap.cpp
+++ b/src/heap.cpp
@@ -1419,7 +1419,8 @@ makeHeap(System* system)
         return Reachable;
       } else if (c.nextGen2.contains(p)
                  or (c.gen2.contains(p)
-                     and c.gen2.indexOf(p) >= c.gen2Base))
+                     and (c.mode == ::MinorCollection
+                          or c.gen2.indexOf(p) >= c.gen2Base)))
       {
         return Tenured;
       } else if (wasCollected(&c, p)) {
diff --git a/src/machine.cpp b/src/machine.cpp
index f1281b4984..32595d35ab 100644
--- a/src/machine.cpp
+++ b/src/machine.cpp
@@ -1341,6 +1341,11 @@ Thread::dispose()
     systemThread = 0;
   }
 
+#ifdef VM_STRESS
+  vm->system->free(heap);
+  heap = 0;
+#endif // VM_STRESS
+
   if (allocator) {
     allocator->free(this);
   }
@@ -1377,7 +1382,8 @@ enter(Thread* t, Thread::State s)
 
   switch (s) {
   case Thread::ExclusiveState: {
-    assert(t, t->state == Thread::ActiveState);
+    assert(t, t->state == Thread::ActiveState
+           or t->state == Thread::ExitState);
 
     while (t->vm->exclusive) {
       // another thread got here first.
diff --git a/src/machine.h b/src/machine.h
index 3a708c1825..1718a5416c 100644
--- a/src/machine.h
+++ b/src/machine.h
@@ -22,7 +22,7 @@
 namespace vm {
 
 const bool Verbose = false;
-const bool DebugRun = true;
+const bool DebugRun = false;
 const bool DebugStack = false;
 const bool DebugMonitors = false;
 
@@ -1221,7 +1221,10 @@ collect(Thread* t, Heap::CollectionType type);
 inline void
 stress(Thread* t)
 {
-  if ((not t->stress) and t->state != Thread::NoState) {
+  if ((not t->stress)
+      and t->state != Thread::NoState
+      and t->state != Thread::IdleState)
+  {
     t->stress = true;
     { ENTER(t, Thread::ExclusiveState);
 
diff --git a/src/run.cpp b/src/run.cpp
index d313449913..bf2d2cb7af 100644
--- a/src/run.cpp
+++ b/src/run.cpp
@@ -396,6 +396,8 @@ invokeNative(Thread* t, object method)
     return VoidField;
   }
 
+  PROTECT(t, data);
+
   pushFrame(t, method);
 
   unsigned count = methodParameterCount(t, method);