Index: compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_mac.cpp
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_mac.cpp
+++ compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_mac.cpp
@@ -29,7 +29,9 @@
 
 class SuspendedThreadsListMac final : public SuspendedThreadsList {
  public:
-  SuspendedThreadsListMac() : threads_(1024) {}
+  SuspendedThreadsListMac() : threads_() {
+    threads_.reserve(1024);
+  }
 
   tid_t GetThreadID(uptr index) const override;
   thread_t GetThread(uptr index) const;