diff --git a/libc/include/sys/ucontext.h b/libc/include/sys/ucontext.h
index 72b8adb..8e5873d 100644
--- a/libc/include/sys/ucontext.h
+++ b/libc/include/sys/ucontext.h
@@ -366,7 +366,10 @@
   unsigned long uc_flags;
   struct ucontext_t* uc_link;
   stack_t uc_stack;
-  sigset_t uc_sigmask;
+  union {
+    sigset_t uc_sigmask;
+    sigset64_t uc_sigmask64;
+  };
   /* The kernel adds extra padding here to allow sigset_t to grow. */
   char __padding[128 - sizeof(sigset_t)];
   mcontext_t uc_mcontext;