diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index 90173aa..9000407 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -78,7 +78,7 @@
 __noreturn void _exit(int __status);
 
 pid_t  fork(void);
-pid_t  vfork(void);
+pid_t  vfork(void) __returns_twice;
 pid_t  getpid(void);
 pid_t  gettid(void) __attribute_const__;
 pid_t  getpgid(pid_t __pid);