diff --git a/libc/private/thread_private.h b/libc/private/thread_private.h
index 2e3ac3d..0081ad0 100644
--- a/libc/private/thread_private.h
+++ b/libc/private/thread_private.h
@@ -50,6 +50,8 @@
 #define _ARC4_UNLOCK() _thread_arc4_unlock()
 #define _ARC4_ATFORK(f) pthread_atfork(NULL, NULL, (f))
 
+extern volatile sig_atomic_t _rs_forked;
+
 __END_DECLS
 
 #endif /* _THREAD_PRIVATE_H_ */