diff --git a/lib/libc/sys/sigaltstack.2 b/lib/libc/sys/sigaltstack.2
index 6119c6a3abce..d9cb27362592 100644
--- a/lib/libc/sys/sigaltstack.2
+++ b/lib/libc/sys/sigaltstack.2
@@ -104,7 +104,7 @@ if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL)
 	/* error return */
 sigstk.ss_size = SIGSTKSZ;
 sigstk.ss_flags = 0;
-if (sigaltstack(&sigstk,0) < 0)
+if (sigaltstack(&sigstk, NULL) < 0)
 	perror("sigaltstack");
 .Ed
 An alternative approach is provided for programs with signal handlers