Index: src/thread.cpp
===================================================================
--- src/thread.cpp
+++ src/thread.cpp
@@ -46,14 +46,17 @@
 void
 thread::join()
 {
-    int ec = __libcpp_thread_join(&__t_);
+    int ec = EINVAL;
+    if (__t_ != 0)
+    {
+        ec = __libcpp_thread_join(&__t_);
+        if (ec == 0)
+            __t_ = 0;
+    }
 #ifndef _LIBCPP_NO_EXCEPTIONS
     if (ec)
         throw system_error(error_code(ec, system_category()), "thread::join failed");
-#else
-    (void)ec;
 #endif  // _LIBCPP_NO_EXCEPTIONS
-    __t_ = 0;
 }
 
 void