diff --git a/libc/bionic/pthread_create.cpp b/libc/bionic/pthread_create.cpp
index 4f7ac2b..d4a8bef 100644
--- a/libc/bionic/pthread_create.cpp
+++ b/libc/bionic/pthread_create.cpp
@@ -300,6 +300,7 @@
   thread->mmap_size = mapping.mmap_size;
   thread->mmap_base_unguarded = mapping.mmap_base_unguarded;
   thread->mmap_size_unguarded = mapping.mmap_size_unguarded;
+  thread->stack_top = reinterpret_cast<uintptr_t>(stack_top);
 
   *tcbp = tcb;
   *child_stack = stack_top;