diff --git a/libc/bionic/pthread_internal.h b/libc/bionic/pthread_internal.h
index 6ace301..8da99dd 100644
--- a/libc/bionic/pthread_internal.h
+++ b/libc/bionic/pthread_internal.h
@@ -29,6 +29,7 @@
 #define _PTHREAD_INTERNAL_H_
 
 #include <pthread.h>
+#include <stdatomic.h>
 
 #include "private/bionic_tls.h"
 
@@ -46,6 +47,13 @@
   void* data;
 };
 
+enum ThreadJoinState {
+  THREAD_NOT_JOINED,
+  THREAD_EXITED_NOT_JOINED,
+  THREAD_JOINED,
+  THREAD_DETACHED
+};
+
 struct pthread_internal_t {
   struct pthread_internal_t* next;
   struct pthread_internal_t* prev;
@@ -74,6 +82,8 @@
 
   pthread_attr_t attr;
 
+  _Atomic(ThreadJoinState) join_state;
+
   __pthread_cleanup_t* cleanup_stack;
 
   void* (*start_routine)(void*);