diff --git a/core/AmThread.cpp b/core/AmThread.cpp
index 868d5c1e..49d37bf5 100644
--- a/core/AmThread.cpp
+++ b/core/AmThread.cpp
@@ -82,9 +82,18 @@ void AmThread::stop()
 
 void AmThread::join()
 {
-  // only when neither stopped nor joined
-  if (_td.joinable())
-    _td.join();
+  // don't attempt to join thread that doesn't exist
+  if (_state == state::idle)
+    return;
+
+  // make sure only one other thread joins this one. all others
+  // are made to wait through the mutex
+  std::lock_guard<std::mutex> _l(_join_mt);
+  if (!_joined) {
+    if (_td.joinable())
+      _td.join();
+    _joined = true;
+  }
 }
 
 
diff --git a/core/AmThread.h b/core/AmThread.h
index eb152cb1..39723dea 100644
--- a/core/AmThread.h
+++ b/core/AmThread.h
@@ -122,6 +122,9 @@ class AmThread
 
   std::atomic<state> _state;
 
+  std::mutex _join_mt;
+  bool _joined;
+
   void _start();
 
 protected:
@@ -135,7 +138,8 @@ public:
   unsigned long _pid;
 
   AmThread()
-    : _state(state::idle)
+    : _state(state::idle),
+      _joined(false)
   {}
 
   virtual ~AmThread();