diff --git a/src/jnienv.cpp b/src/jnienv.cpp
index 7bda0458ad..0b1b34760e 100644
--- a/src/jnienv.cpp
+++ b/src/jnienv.cpp
@@ -77,8 +77,17 @@ DetachCurrentThread(Machine* m)
 {
   Thread* t = static_cast<Thread*>(m->localThread->get());
   if (t) {
+    expect(t, t != m->rootThread);
+
     m->localThread->set(0);
-    t->exit();
+
+    ACQUIRE_RAW(t, t->m->stateLock);
+
+    enter(t, Thread::ActiveState);
+    enter(t, Thread::ZombieState);
+
+    t->state = Thread::JoinedState;
+
     return 0;
   } else {
     return -1;
diff --git a/src/posix.cpp b/src/posix.cpp
index 5f2fbf11c4..48096dac52 100644
--- a/src/posix.cpp
+++ b/src/posix.cpp
@@ -129,7 +129,7 @@ class MySystem: public System {
 
     virtual void join() {
       int rv UNUSED = pthread_join(thread, 0);
-      //expect(s, rv == 0);
+      expect(s, rv == 0);
     }
 
     virtual void dispose() {