diff --git a/libc/bionic/pthread_exit.cpp b/libc/bionic/pthread_exit.cpp
index ceda931..6b68bb7 100644
--- a/libc/bionic/pthread_exit.cpp
+++ b/libc/bionic/pthread_exit.cpp
@@ -81,8 +81,7 @@
 
   if (thread->alternate_signal_stack != NULL) {
     // Tell the kernel to stop using the alternate signal stack.
-    stack_t ss;
-    ss.ss_sp = NULL;
+    stack_t ss = {};
     ss.ss_flags = SS_DISABLE;
     sigaltstack(&ss, NULL);