diff --git a/libc/include/sys/linux-unistd.h b/libc/include/sys/linux-unistd.h
index f48dbcd..d6f706b 100644
--- a/libc/include/sys/linux-unistd.h
+++ b/libc/include/sys/linux-unistd.h
@@ -48,6 +48,7 @@
 int              prctl (int option, unsigned int arg2, unsigned int arg3, unsigned int arg4, unsigned int arg5);
 int              capget (cap_user_header_t header, cap_user_data_t data);
 int              capset (cap_user_header_t header, const cap_user_data_t data);
+int              sigaltstack (const stack_t*, stack_t*);
 int              acct (const char*  filepath);
 ssize_t          read (int, void*, size_t);
 ssize_t          write (int, const void*, size_t);