diff --git a/STYLE.md b/STYLE.md
index 2f4624ad4e22f..b5767ae812949 100644
--- a/STYLE.md
+++ b/STYLE.md
@@ -63,6 +63,10 @@
   NiceMock for mocks whose behavior is not the focus of a test.
 * There are probably a few other things missing from this list. We will add them as they
   are brought to our attention.
+* [Thread
+  annotations](https://github.com/abseil/abseil-cpp/blob/master/absl/base/thread_annotations.h),
+  such as `GUARDED_BY`, should be used for shared state guarded by
+  locks/mutexes.
 
 # Error handling
 
diff --git a/source/common/common/BUILD b/source/common/common/BUILD
index 19ec24be5691c..7fc5586f92fd2 100644
--- a/source/common/common/BUILD
+++ b/source/common/common/BUILD
@@ -109,6 +109,12 @@ envoy_cc_library(
     hdrs = ["stl_helpers.h"],
 )
 
+envoy_cc_library(
+    name = "thread_annotations",
+    hdrs = ["thread_annotations.h"],
+    external_deps = ["abseil_base"],
+)
+
 envoy_cc_library(
     name = "thread_lib",
     srcs = ["thread.cc"],
diff --git a/source/common/common/thread_annotations.h b/source/common/common/thread_annotations.h
new file mode 100644
index 0000000000000..bcdfb3ea1c703
--- /dev/null
+++ b/source/common/common/thread_annotations.h
@@ -0,0 +1,11 @@
+#pragma once
+
+// NOLINT(namespace-envoy)
+
+#include "absl/base/thread_annotations.h"
+
+#ifdef __APPLE__
+#undef THREAD_ANNOTATION_ATTRIBUTE__
+// See #2571, we get problematic warnings on Clang + OS X.
+#define THREAD_ANNOTATION_ATTRIBUTE__(x) // no-op
+#endif
diff --git a/source/common/grpc/BUILD b/source/common/grpc/BUILD
index 46174a1441acc..bbc466cf38f6b 100644
--- a/source/common/grpc/BUILD
+++ b/source/common/grpc/BUILD
@@ -85,6 +85,7 @@ envoy_cc_library(
         "//include/envoy/thread_local:thread_local_interface",
         "//source/common/common:empty_string",
         "//source/common/common:linked_object",
+        "//source/common/common:thread_annotations",
         "//source/common/common:thread_lib",
         "//source/common/tracing:http_tracer_lib",
     ],
diff --git a/source/common/grpc/google_async_client_impl.h b/source/common/grpc/google_async_client_impl.h
index 89ad4ab80dbbb..56939a7f23233 100644
--- a/source/common/grpc/google_async_client_impl.h
+++ b/source/common/grpc/google_async_client_impl.h
@@ -8,6 +8,7 @@
 
 #include "common/common/linked_object.h"
 #include "common/common/thread.h"
+#include "common/common/thread_annotations.h"
 #include "common/tracing/http_tracer_impl.h"
 
 #include "grpc++/generic/generic_stub.h"
@@ -289,7 +290,8 @@ class GoogleAsyncStreamImpl : public AsyncStream,
   uint32_t inflight_tags_{};
   // Queue of completed (op, ok) passed from completionThread() to
   // handleOpCompletion().
-  std::deque<std::pair<GoogleAsyncTag::Operation, bool>> completed_ops_;
+  std::deque<std::pair<GoogleAsyncTag::Operation, bool>>
+      completed_ops_ GUARDED_BY(completed_ops_lock_);
   std::mutex completed_ops_lock_;
 
   friend class GoogleAsyncClientImpl;