diff --git a/src/core/tls.h b/src/core/tls.h
index c4e3080a4..46ca8153b 100644
--- a/src/core/tls.h
+++ b/src/core/tls.h
@@ -44,9 +44,9 @@ Tcb* GetTcbBase();
 void EnsureThreadInitialized();
 
 template <size_t size>
-void ClearStack() {
-    void* buf = alloca(size);
-    memset(buf, 0, size);
+__attribute__((optnone)) void ClearStack() {
+    volatile void* buf = alloca(size);
+    memset(const_cast<void*>(buf), 0, size);
     buf = nullptr;
 }