diff --git a/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.member/join.pass.cpp b/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.member/join.pass.cpp
--- a/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.member/join.pass.cpp
+++ b/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.member/join.pass.cpp
@@ -23,6 +23,8 @@
 #include "make_test_thread.h"
 #include "test_macros.h"
 
+std::atomic_bool done(false);
+
 class G
 {
     int alive_;
@@ -45,7 +47,7 @@
 int G::n_alive = 0;
 bool G::op_run = false;
 
-void foo() {}
+void foo() { done = true; }
 
 int main(int, char**)
 {
@@ -72,6 +74,11 @@
             assert(false);
         } catch (std::system_error const&) {
         }
+        // Wait to make sure that the detached thread has started up.
+        // Without this, we could exit main and start destructing global
+        // resources that are needed when the thread starts up, while the
+        // detached thread would start up only later.
+        while (!done) {}
     }
 #endif