diff --git a/db/column_family.cc b/db/column_family.cc
index 2be22bd86..8857f5c09 100644
--- a/db/column_family.cc
+++ b/db/column_family.cc
@@ -469,7 +469,7 @@ ColumnFamilyData::~ColumnFamilyData() {
     local_sv_.reset();
     super_version_->db_mutex->Lock();
 
-    bool is_last_reference __attribute__((unused));
+    bool is_last_reference __attribute__((__unused__));
     is_last_reference = super_version_->Unref();
     assert(is_last_reference);
     super_version_->Cleanup();
@@ -480,7 +480,7 @@ ColumnFamilyData::~ColumnFamilyData() {
   if (dummy_versions_ != nullptr) {
     // List must be empty
     assert(dummy_versions_->TEST_Next() == dummy_versions_);
-    bool deleted __attribute__((unused));
+    bool deleted __attribute__((__unused__));
     deleted = dummy_versions_->Unref();
     assert(deleted);
   }
diff --git a/db/db_impl_compaction_flush.cc b/db/db_impl_compaction_flush.cc
index 6776a2478..d834dddc7 100644
--- a/db/db_impl_compaction_flush.cc
+++ b/db/db_impl_compaction_flush.cc
@@ -1695,7 +1695,7 @@ Status DBImpl::BackgroundCompaction(bool* made_progress,
     env_->Schedule(&DBImpl::BGWorkBottomCompaction, ca, Env::Priority::BOTTOM,
                    this, &DBImpl::UnscheduleCallback);
   } else {
-    int output_level  __attribute__((unused));
+    int output_level  __attribute__((__unused__));
     output_level = c->output_level();
     TEST_SYNC_POINT_CALLBACK("DBImpl::BackgroundCompaction:NonTrivial",
                              &output_level);
diff --git a/db/version_set.cc b/db/version_set.cc
index 3226304de..4af335590 100644
--- a/db/version_set.cc
+++ b/db/version_set.cc
@@ -1976,7 +1976,7 @@ void VersionStorageInfo::ExtendFileRangeOverlappingInterval(
 #endif
   *start_index = mid_index + 1;
   *end_index = mid_index;
-  int count __attribute__((unused));
+  int count __attribute__((__unused__));
   count = 0;
 
   // check backwards from 'mid' to lower indices
diff --git a/env/io_posix.cc b/env/io_posix.cc
index b00def45f..e2190670a 100644
--- a/env/io_posix.cc
+++ b/env/io_posix.cc
@@ -799,7 +799,7 @@ Status PosixWritableFile::Close() {
     // trim the extra space preallocated at the end of the file
     // NOTE(ljin): we probably don't want to surface failure as an IOError,
     // but it will be nice to log these errors.
-    int dummy __attribute__((unused));
+    int dummy __attribute__((__unused__));
     dummy = ftruncate(fd_, filesize_);
 #if defined(ROCKSDB_FALLOCATE_PRESENT) && !defined(TRAVIS)
     // in some file systems, ftruncate only trims trailing space if the
diff --git a/monitoring/thread_status_updater.cc b/monitoring/thread_status_updater.cc
index 78c8afa1c..23e318c0c 100644
--- a/monitoring/thread_status_updater.cc
+++ b/monitoring/thread_status_updater.cc
@@ -252,7 +252,7 @@ void ThreadStatusUpdater::EraseColumnFamilyInfo(const void* cf_key) {
     ConstantColumnFamilyInfo& cf_info = cf_pair->second;
     auto db_pair = db_key_map_.find(cf_info.db_key);
     assert(db_pair != db_key_map_.end());
-    size_t result __attribute__((unused));
+    size_t result __attribute__((__unused__));
     result = db_pair->second.erase(cf_key);
     assert(result);
     cf_info_map_.erase(cf_pair);
diff --git a/monitoring/thread_status_updater_debug.cc b/monitoring/thread_status_updater_debug.cc
index d4fd4ea23..358e105e4 100644
--- a/monitoring/thread_status_updater_debug.cc
+++ b/monitoring/thread_status_updater_debug.cc
@@ -21,7 +21,7 @@ void ThreadStatusUpdater::TEST_VerifyColumnFamilyInfoMap(
   }
   for (auto* handle : handles) {
     auto* cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(handle)->cfd();
-    auto iter __attribute__((unused)) = cf_info_map_.find(cfd);
+    auto iter __attribute__((__unused__)) = cf_info_map_.find(cfd);
     if (check_exist) {
       assert(iter != cf_info_map_.end());
       assert(iter->second.cf_name == cfd->GetName());
diff --git a/port/win/env_win.cc b/port/win/env_win.cc
index 5073944f5..8cf61e52d 100644
--- a/port/win/env_win.cc
+++ b/port/win/env_win.cc
@@ -74,8 +74,7 @@ WinEnvIO::WinEnvIO(Env* hosted_env)
 
   {
     LARGE_INTEGER qpf;
-    // No init as the compiler complains about unused var
-    BOOL ret;
+    BOOL ret __attribute__((__unused__));
     ret = QueryPerformanceFrequency(&qpf);
     assert(ret == TRUE);
     perf_counter_frequency_ = qpf.QuadPart;
diff --git a/port/win/io_win.cc b/port/win/io_win.cc
index 39af72368..7d83896c6 100644
--- a/port/win/io_win.cc
+++ b/port/win/io_win.cc
@@ -192,8 +192,8 @@ WinMmapReadableFile::WinMmapReadableFile(const std::string& fileName,
       length_(length) {}
 
 WinMmapReadableFile::~WinMmapReadableFile() {
-  BOOL ret = ::UnmapViewOfFile(mapped_region_);
-  (void)ret;
+  BOOL ret __attribute__((__unused__));
+  ret = ::UnmapViewOfFile(mapped_region_);
   assert(ret);
 
   ret = ::CloseHandle(hMap_);
@@ -279,7 +279,7 @@ Status WinMmapFile::MapNewRegion() {
 
     if (hMap_ != NULL) {
       // Unmap the previous one
-      BOOL ret;
+      BOOL ret __attribute__((__unused__));
       ret = ::CloseHandle(hMap_);
       assert(ret);
       hMap_ = NULL;
@@ -1023,7 +1023,7 @@ Status WinDirectory::Fsync() { return Status::OK(); }
 /// WinFileLock
 
 WinFileLock::~WinFileLock() {
-  BOOL ret;
+  BOOL ret __attribute__((__unused__));
   ret = ::CloseHandle(hFile_);
   assert(ret);
 }
diff --git a/tools/db_bench_tool.cc b/tools/db_bench_tool.cc
index 28807eea9..38f731690 100644
--- a/tools/db_bench_tool.cc
+++ b/tools/db_bench_tool.cc
@@ -350,7 +350,7 @@ DEFINE_uint64(subcompactions, 1,
               "Maximum number of subcompactions to divide L0-L1 compactions "
               "into.");
 static const bool FLAGS_subcompactions_dummy
-    __attribute__((unused)) = RegisterFlagValidator(&FLAGS_subcompactions,
+    __attribute__((__unused__)) = RegisterFlagValidator(&FLAGS_subcompactions,
                                                     &ValidateUint32Range);
 
 DEFINE_int32(max_background_flushes,
@@ -766,7 +766,7 @@ static bool ValidateCompressionLevel(const char* flagname, int32_t value) {
   return true;
 }
 
-static const bool FLAGS_compression_level_dummy __attribute__((unused)) =
+static const bool FLAGS_compression_level_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_compression_level, &ValidateCompressionLevel);
 
 DEFINE_int32(min_level_to_compress, -1, "If non-negative, compression starts"
@@ -1037,31 +1037,31 @@ DEFINE_int32(skip_list_lookahead, 0, "Used with skip_list memtablerep; try "
 DEFINE_bool(report_file_operations, false, "if report number of file "
             "operations");
 
-static const bool FLAGS_soft_rate_limit_dummy __attribute__((unused)) =
+static const bool FLAGS_soft_rate_limit_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_soft_rate_limit, &ValidateRateLimit);
 
-static const bool FLAGS_hard_rate_limit_dummy __attribute__((unused)) =
+static const bool FLAGS_hard_rate_limit_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_hard_rate_limit, &ValidateRateLimit);
 
-static const bool FLAGS_prefix_size_dummy __attribute__((unused)) =
+static const bool FLAGS_prefix_size_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_prefix_size, &ValidatePrefixSize);
 
-static const bool FLAGS_key_size_dummy __attribute__((unused)) =
+static const bool FLAGS_key_size_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_key_size, &ValidateKeySize);
 
-static const bool FLAGS_cache_numshardbits_dummy __attribute__((unused)) =
+static const bool FLAGS_cache_numshardbits_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_cache_numshardbits,
                           &ValidateCacheNumshardbits);
 
-static const bool FLAGS_readwritepercent_dummy __attribute__((unused)) =
+static const bool FLAGS_readwritepercent_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_readwritepercent, &ValidateInt32Percent);
 
 DEFINE_int32(disable_seek_compaction, false,
              "Not used, left here for backwards compatibility");
 
-static const bool FLAGS_deletepercent_dummy __attribute__((unused)) =
+static const bool FLAGS_deletepercent_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_deletepercent, &ValidateInt32Percent);
-static const bool FLAGS_table_cache_numshardbits_dummy __attribute__((unused)) =
+static const bool FLAGS_table_cache_numshardbits_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_table_cache_numshardbits,
                           &ValidateTableCacheNumshardbits);
 
diff --git a/tools/db_stress.cc b/tools/db_stress.cc
index d972bf6da..f24764b69 100644
--- a/tools/db_stress.cc
+++ b/tools/db_stress.cc
@@ -90,7 +90,7 @@ static bool ValidateUint32Range(const char* flagname, uint64_t value) {
 }
 
 DEFINE_uint64(seed, 2341234, "Seed for PRNG");
-static const bool FLAGS_seed_dummy __attribute__((unused)) =
+static const bool FLAGS_seed_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_seed, &ValidateUint32Range);
 
 DEFINE_int64(max_key, 1 * KB* KB,
@@ -270,7 +270,7 @@ DEFINE_bool(allow_concurrent_memtable_write, false,
 DEFINE_bool(enable_write_thread_adaptive_yield, true,
             "Use a yielding spin loop for brief writer thread waits.");
 
-static const bool FLAGS_subcompactions_dummy __attribute__((unused)) =
+static const bool FLAGS_subcompactions_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_subcompactions, &ValidateUint32Range);
 
 static bool ValidateInt32Positive(const char* flagname, int32_t value) {
@@ -282,7 +282,7 @@ static bool ValidateInt32Positive(const char* flagname, int32_t value) {
   return true;
 }
 DEFINE_int32(reopen, 10, "Number of times database reopens");
-static const bool FLAGS_reopen_dummy __attribute__((unused)) =
+static const bool FLAGS_reopen_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_reopen, &ValidateInt32Positive);
 
 DEFINE_int32(bloom_bits, 10, "Bloom filter bits per key. "
@@ -320,7 +320,7 @@ DEFINE_bool(use_fsync, false, "If true, issue fsync instead of fdatasync");
 DEFINE_int32(kill_random_test, 0,
              "If non-zero, kill at various points in source code with "
              "probability 1/this");
-static const bool FLAGS_kill_random_test_dummy __attribute__((unused)) =
+static const bool FLAGS_kill_random_test_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_kill_random_test, &ValidateInt32Positive);
 extern int rocksdb_kill_odds;
 
@@ -380,29 +380,29 @@ static bool ValidateInt32Percent(const char* flagname, int32_t value) {
 
 DEFINE_int32(readpercent, 10,
              "Ratio of reads to total workload (expressed as a percentage)");
-static const bool FLAGS_readpercent_dummy __attribute__((unused)) =
+static const bool FLAGS_readpercent_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_readpercent, &ValidateInt32Percent);
 
 DEFINE_int32(prefixpercent, 20,
              "Ratio of prefix iterators to total workload (expressed as a"
              " percentage)");
-static const bool FLAGS_prefixpercent_dummy __attribute__((unused)) =
+static const bool FLAGS_prefixpercent_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_prefixpercent, &ValidateInt32Percent);
 
 DEFINE_int32(writepercent, 45,
              "Ratio of writes to total workload (expressed as a percentage)");
-static const bool FLAGS_writepercent_dummy __attribute__((unused)) =
+static const bool FLAGS_writepercent_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_writepercent, &ValidateInt32Percent);
 
 DEFINE_int32(delpercent, 15,
              "Ratio of deletes to total workload (expressed as a percentage)");
-static const bool FLAGS_delpercent_dummy __attribute__((unused)) =
+static const bool FLAGS_delpercent_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_delpercent, &ValidateInt32Percent);
 
 DEFINE_int32(delrangepercent, 0,
              "Ratio of range deletions to total workload (expressed as a "
              "percentage). Cannot be used with test_batches_snapshots");
-static const bool FLAGS_delrangepercent_dummy __attribute__((unused)) =
+static const bool FLAGS_delrangepercent_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_delrangepercent, &ValidateInt32Percent);
 
 DEFINE_int32(nooverwritepercent, 60,
@@ -413,11 +413,11 @@ static const bool FLAGS_nooverwritepercent_dummy __attribute__((__unused__)) =
 
 DEFINE_int32(iterpercent, 10, "Ratio of iterations to total workload"
              " (expressed as a percentage)");
-static const bool FLAGS_iterpercent_dummy __attribute__((unused)) =
+static const bool FLAGS_iterpercent_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_iterpercent, &ValidateInt32Percent);
 
 DEFINE_uint64(num_iterations, 10, "Number of iterations per MultiIterate run");
-static const bool FLAGS_num_iterations_dummy __attribute__((unused)) =
+static const bool FLAGS_num_iterations_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_num_iterations, &ValidateUint32Range);
 
 namespace {
@@ -494,11 +494,11 @@ DEFINE_string(hdfs, "", "Name of hdfs environment");
 static rocksdb::Env* FLAGS_env = rocksdb::Env::Default();
 
 DEFINE_uint64(ops_per_thread, 1200000, "Number of operations per thread.");
-static const bool FLAGS_ops_per_thread_dummy __attribute__((unused)) =
+static const bool FLAGS_ops_per_thread_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_ops_per_thread, &ValidateUint32Range);
 
 DEFINE_uint64(log2_keys_per_lock, 2, "Log2 of number of keys per lock");
-static const bool FLAGS_log2_keys_per_lock_dummy __attribute__((unused)) =
+static const bool FLAGS_log2_keys_per_lock_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_log2_keys_per_lock, &ValidateUint32Range);
 
 DEFINE_bool(in_place_update, false, "On true, does inplace update in memtable");
@@ -537,7 +537,7 @@ static bool ValidatePrefixSize(const char* flagname, int32_t value) {
   return true;
 }
 DEFINE_int32(prefix_size, 7, "Control the prefix size for HashSkipListRep");
-static const bool FLAGS_prefix_size_dummy __attribute__((unused)) =
+static const bool FLAGS_prefix_size_dummy __attribute__((__unused__)) =
     RegisterFlagValidator(&FLAGS_prefix_size, &ValidatePrefixSize);
 
 DEFINE_bool(use_merge, false, "On true, replaces all writes with a Merge "
@@ -1789,7 +1789,7 @@ class StressTest {
                 cf, new_name.c_str());
           }
           thread->shared->LockColumnFamily(cf);
-          Status s __attribute__((unused));
+          Status s __attribute__((__unused__));
           s = db_->DropColumnFamily(column_families_[cf]);
           delete column_families_[cf];
           if (!s.ok()) {
diff --git a/utilities/document/document_db.cc b/utilities/document/document_db.cc
index 0dadc99a0..90b21bbe7 100644
--- a/utilities/document/document_db.cc
+++ b/utilities/document/document_db.cc
@@ -922,7 +922,7 @@ class DocumentDBImpl : public DocumentDB {
       for (const auto& update : updates.Items()) {
         if (update.first == "$set") {
           JSONDocumentBuilder builder;
-          bool res __attribute__((unused)) = builder.WriteStartObject();
+          bool res __attribute__((__unused__)) = builder.WriteStartObject();
           assert(res);
           for (const auto& itr : update.second.Items()) {
             if (itr.first == kPrimaryKey) {
diff --git a/utilities/document/json_document.cc b/utilities/document/json_document.cc
index fe7fbab16..21a4c7dbc 100644
--- a/utilities/document/json_document.cc
+++ b/utilities/document/json_document.cc
@@ -46,9 +46,9 @@ void InitJSONDocument(std::unique_ptr<char[]>* data,
                       Func f) {
   // TODO(stash): maybe add function to FbsonDocument to avoid creating array?
   fbson::FbsonWriter writer;
-  bool res __attribute__((unused)) = writer.writeStartArray();
+  bool res __attribute__((__unused__)) = writer.writeStartArray();
   assert(res);
-  uint32_t bytesWritten __attribute__((unused));
+  uint32_t bytesWritten __attribute__((__unused__));
   bytesWritten = f(writer);
   assert(bytesWritten != 0);
   res = writer.writeEndArray();
@@ -68,7 +68,7 @@ void InitString(std::unique_ptr<char[]>* data,
                 const std::string& s) {
   InitJSONDocument(data, value, std::bind(
       [](fbson::FbsonWriter& writer, const std::string& str) -> uint32_t {
-        bool res __attribute__((unused)) = writer.writeStartString();
+        bool res __attribute__((__unused__)) = writer.writeStartString();
         assert(res);
         auto bytesWritten = writer.writeString(str.c_str(),
                             static_cast<uint32_t>(str.length()));
@@ -114,7 +114,7 @@ bool IsComparable(fbson::FbsonValue* left, fbson::FbsonValue* right) {
 
 void CreateArray(std::unique_ptr<char[]>* data, fbson::FbsonValue** value) {
   fbson::FbsonWriter writer;
-  bool res __attribute__((unused)) = writer.writeStartArray();
+  bool res __attribute__((__unused__)) = writer.writeStartArray();
   assert(res);
   res = writer.writeEndArray();
   assert(res);
@@ -127,7 +127,7 @@ void CreateArray(std::unique_ptr<char[]>* data, fbson::FbsonValue** value) {
 
 void CreateObject(std::unique_ptr<char[]>* data, fbson::FbsonValue** value) {
   fbson::FbsonWriter writer;
-  bool res __attribute__((unused)) = writer.writeStartObject();
+  bool res __attribute__((__unused__)) = writer.writeStartObject();
   assert(res);
   res = writer.writeEndObject();
   assert(res);
diff --git a/utilities/lua/rocks_lua_compaction_filter.cc b/utilities/lua/rocks_lua_compaction_filter.cc
index 0934ca9c9..c635a0fb4 100644
--- a/utilities/lua/rocks_lua_compaction_filter.cc
+++ b/utilities/lua/rocks_lua_compaction_filter.cc
@@ -158,7 +158,7 @@ const char* RocksLuaCompactionFilter::Name() const {
         "return value is not a string while string is expected");
   } else {
     const char* name_buf = lua_tostring(lua_state, -1);
-    const size_t name_size __attribute__((unused)) = lua_strlen(lua_state, -1);
+    const size_t name_size __attribute__((__unused__)) = lua_strlen(lua_state, -1);
     assert(name_buf[name_size] == '\0');
     assert(strlen(name_buf) <= name_size);
     name_ = name_buf;
diff --git a/utilities/transactions/transaction_base.cc b/utilities/transactions/transaction_base.cc
index c3dbd5cc7..3539c7431 100644
--- a/utilities/transactions/transaction_base.cc
+++ b/utilities/transactions/transaction_base.cc
@@ -623,7 +623,7 @@ void TransactionBaseImpl::UndoGetForUpdate(ColumnFamilyHandle* column_family,
   auto& cf_tracked_keys = tracked_keys_[column_family_id];
   std::string key_str = key.ToString();
   bool can_decrement = false;
-  bool can_unlock __attribute__((unused)) = false;
+  bool can_unlock __attribute__((__unused__)) = false;
 
   if (save_points_ != nullptr && !save_points_->empty()) {
     // Check if this key was fetched ForUpdate in this SavePoint