diff --git a/libc/include/signal.h b/libc/include/signal.h
index 7bc3145..4401164 100644
--- a/libc/include/signal.h
+++ b/libc/include/signal.h
@@ -120,6 +120,7 @@
 extern int raise(int);
 extern int kill(pid_t, int);
 extern int killpg(int pgrp, int sig);
+extern int sigaltstack(const stack_t *ss, stack_t *oss);
 
 
 __END_DECLS