diff --git a/v8/src/profiler/profile-generator.cc b/v8/src/profiler/profile-generator.cc
--- a/v8/src/profiler/profile-generator.cc
+++ b/v8/src/profiler/profile-generator.cc
@@ -269,8 +269,15 @@ CpuProfileDeoptInfo CodeEntry::GetDeoptInfo() {
 }

 CodeEntry::RareData* CodeEntry::EnsureRareData() {
   if (!rare_data_) {
-    rare_data_.reset(new RareData());
+    // rare_data_ is published from the SamplingEventsProcessor thread (via
+    // CodeDisableOpt/CodeDeopt event handling) and read on the main thread in
+    // bailout_reason()/has_deopt_info() while serializing a stopped profile
+    // that is not the last one (processor thread still running). Ensure the
+    // RareData constructor's field stores are visible before the pointer is.
+    RareData* rd = new RareData();
+    std::atomic_thread_fence(std::memory_order_release);
+    rare_data_.reset(rd);
   }
   return rare_data_.get();
 }