diff --git a/libc/bionic/libc_init_common.cpp b/libc/bionic/libc_init_common.cpp
index 15b3fd5..94b7dd2 100644
--- a/libc/bionic/libc_init_common.cpp
+++ b/libc/bionic/libc_init_common.cpp
@@ -85,8 +85,10 @@
   // because things like environment variables with global scope live on it.
   // We also can't free the pthread_internal_t itself, since that lives on the main
   // thread's stack rather than on the heap.
+  // The main thread has no mmap allocated space for stack or pthread_internal_t.
+  main_thread.mmap_size = 0;
   pthread_attr_init(&main_thread.attr);
-  main_thread.attr.flags = PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK | PTHREAD_ATTR_FLAG_MAIN_THREAD;
+  main_thread.attr.flags = PTHREAD_ATTR_FLAG_MAIN_THREAD;
   main_thread.attr.guard_size = 0; // The main thread has no guard page.
   main_thread.attr.stack_size = 0; // User code should never see this; we'll compute it when asked.
   // TODO: the main thread's sched_policy and sched_priority need to be queried.