diff --git a/libc/bionic/pthread_internal.h b/libc/bionic/pthread_internal.h
index 22cc400..22b0558 100644
--- a/libc/bionic/pthread_internal.h
+++ b/libc/bionic/pthread_internal.h
@@ -98,6 +98,7 @@
   void* (*start_routine)(void*);
   void* start_routine_arg;
   void* return_value;
+  sigset64_t start_mask;
 
   void* alternate_signal_stack;