diff --git a/libc/bionic/pthread_internals.cpp b/libc/bionic/pthread_internals.cpp
index f8afeaf..09c48dc 100644
--- a/libc/bionic/pthread_internals.cpp
+++ b/libc/bionic/pthread_internals.cpp
@@ -48,7 +48,7 @@
 
   // The main thread is not heap-allocated. See __libc_init_tls for the declaration,
   // and __libc_init_common for the point where it's added to the thread list.
-  if (thread->allocated_on_heap) {
+  if ((thread->attr.flags & PTHREAD_ATTR_FLAG_MAIN_THREAD) == 0) {
     free(thread);
   }
 }