diff --git a/async_grpc/completion_queue_pool.cc b/async_grpc/completion_queue_pool.cc
index a32d0c0..580576d 100644
--- a/async_grpc/completion_queue_pool.cc
+++ b/async_grpc/completion_queue_pool.cc
@@ -38,7 +38,9 @@ void CompletionQueue::Shutdown() {
   CHECK(thread_) << "CompletionQueue not yet started.";
   LOG(INFO) << "Shutting down client completion queue " << this;
   completion_queue_.Shutdown();
-  thread_->join();
+  if (thread_->joinable()) {
+    thread_->join();
+  }
 }
 
 void CompletionQueue::RunCompletionQueue() {
diff --git a/async_grpc/completion_queue_thread.cc b/async_grpc/completion_queue_thread.cc
index d900548..75e7fb5 100644
--- a/async_grpc/completion_queue_thread.cc
+++ b/async_grpc/completion_queue_thread.cc
@@ -38,7 +38,9 @@ void CompletionQueueThread::Start(CompletionQueueRunner runner) {
 void CompletionQueueThread::Shutdown() {
   LOG(INFO) << "Shutting down completion queue " << completion_queue_.get();
   completion_queue_->Shutdown();
-  worker_thread_->join();
+  if (worker_thread_->joinable()) {
+    worker_thread_->join();
+  }
 }
 
 }  // namespace async_grpc
diff --git a/async_grpc/event_queue_thread.cc b/async_grpc/event_queue_thread.cc
index d13f117..f46c1e8 100644
--- a/async_grpc/event_queue_thread.cc
+++ b/async_grpc/event_queue_thread.cc
@@ -36,7 +36,9 @@ void EventQueueThread::Start(EventQueueRunner runner) {
 
 void EventQueueThread::Shutdown() {
   LOG(INFO) << "Shutting down event queue " << event_queue_.get();
-  thread_->join();
+  if (thread_->joinable()) {
+    thread_->join();
+  }
 }
 
 }  // namespace async_grpc