Index: lib/asan/asan_thread.cc
===================================================================
--- lib/asan/asan_thread.cc
+++ lib/asan/asan_thread.cc
@@ -477,6 +477,11 @@
   __asan::asanThreadRegistry().Unlock();
 }
 
+ThreadRegistry *GetThreadRegistryLocked() {
+  __asan::asanThreadRegistry().CheckLocked();
+  return &__asan::asanThreadRegistry();
+}
+
 void EnsureMainThreadIDIsCorrect() {
   __asan::EnsureMainThreadIDIsCorrect();
 }
Index: lib/lsan/lsan_common.h
===================================================================
--- lib/lsan/lsan_common.h
+++ lib/lsan/lsan_common.h
@@ -47,6 +47,7 @@
 
 namespace __sanitizer {
 class FlagParser;
+class ThreadRegistry;
 struct DTLS;
 }
 
@@ -204,6 +205,7 @@
 // Wrappers for ThreadRegistry access.
 void LockThreadRegistry();
 void UnlockThreadRegistry();
+ThreadRegistry *GetThreadRegistryLocked();
 bool GetThreadRangesLocked(tid_t os_id, uptr *stack_begin, uptr *stack_end,
                            uptr *tls_begin, uptr *tls_end, uptr *cache_begin,
                            uptr *cache_end, DTLS **dtls);
Index: lib/lsan/lsan_common.cc
===================================================================
--- lib/lsan/lsan_common.cc
+++ lib/lsan/lsan_common.cc
@@ -15,14 +15,15 @@
 #include "lsan_common.h"
 
 #include "sanitizer_common/sanitizer_common.h"
-#include "sanitizer_common/sanitizer_flags.h"
 #include "sanitizer_common/sanitizer_flag_parser.h"
+#include "sanitizer_common/sanitizer_flags.h"
 #include "sanitizer_common/sanitizer_placement_new.h"
 #include "sanitizer_common/sanitizer_procmaps.h"
+#include "sanitizer_common/sanitizer_report_decorator.h"
 #include "sanitizer_common/sanitizer_stackdepot.h"
 #include "sanitizer_common/sanitizer_stacktrace.h"
 #include "sanitizer_common/sanitizer_suppressions.h"
-#include "sanitizer_common/sanitizer_report_decorator.h"
+#include "sanitizer_common/sanitizer_thread_registry.h"
 #include "sanitizer_common/sanitizer_tls_get_addr.h"
 
 #if CAN_SANITIZE_LEAKS
@@ -526,11 +527,36 @@
   LeakReport leak_report;
 };
 
+static void ReportIfNotSuspended(ThreadContextBase *tctx, void *arg) {
+  const InternalMmapVector<tid_t> &suspended_threads =
+      *(const InternalMmapVector<tid_t> *)arg;
+  if (tctx->status == ThreadStatusRunning) {
+    uptr i = InternalLowerBound(suspended_threads, 0, suspended_threads.size(),
+                                tctx->os_id, CompareLess<int>());
+    if (i >= suspended_threads.size() || suspended_threads[i] != tctx->os_id)
+      Report("Running thread %d was not suspended. False leaks are possible.\n",
+             tctx->os_id);
+  };
+}
+
+static void ReportUnsuspendedThreads(
+    const SuspendedThreadsList &suspended_threads) {
+  InternalMmapVector<tid_t> threads(suspended_threads.ThreadCount());
+  for (uptr i = 0; i < suspended_threads.ThreadCount(); ++i)
+    threads[i] = suspended_threads.GetThreadID(i);
+
+  Sort(threads.data(), threads.size());
+
+  GetThreadRegistryLocked()->RunCallbackForEachThreadLocked(
+      &ReportIfNotSuspended, &threads);
+}
+
 static void CheckForLeaksCallback(const SuspendedThreadsList &suspended_threads,
                                   void *arg) {
   CheckForLeaksParam *param = reinterpret_cast<CheckForLeaksParam *>(arg);
   CHECK(param);
   CHECK(!param->success);
+  ReportUnsuspendedThreads(suspended_threads);
   ClassifyAllChunks(suspended_threads);
   ForEachChunk(CollectLeaksCb, &param->leak_report);
   // Clean up for subsequent leak checks. This assumes we did not overwrite any
Index: lib/lsan/lsan_thread.cc
===================================================================
--- lib/lsan/lsan_thread.cc
+++ lib/lsan/lsan_thread.cc
@@ -155,4 +155,9 @@
   thread_registry->Unlock();
 }
 
+ThreadRegistry *GetThreadRegistryLocked() {
+  thread_registry->CheckLocked();
+  return thread_registry;
+}
+
 } // namespace __lsan