diff --git a/include/MySQL_Thread.h b/include/MySQL_Thread.h
index b2e7d8b48..f6fdbd5b3 100644
--- a/include/MySQL_Thread.h
+++ b/include/MySQL_Thread.h
@@ -297,7 +297,7 @@ struct p_th_counter {
 		mysql_killed_backend_connections,
 		mysql_killed_backend_queries,
 		client_host_error_killed_connections,
-		__size
+		SIZE_
 	};
 };
 
@@ -327,7 +327,7 @@ struct p_th_gauge {
 		mysql_monitor_replication_lag_interval,
 		mysql_monitor_replication_lag_timeout,
 		mysql_monitor_history,
-		__size
+		SIZE_
 
 	};
 };
@@ -618,8 +618,8 @@ class MySQL_Threads_Handler
 		unsigned int mirror_sessions_current;
 		int threads_initialized = 0;
 		/// Prometheus metrics arrays
-		std::array<prometheus::Counter*, p_th_counter::__size> p_counter_array {};
-		std::array<prometheus::Gauge*, p_th_gauge::__size> p_gauge_array {};
+		std::array<prometheus::Counter*, p_th_counter::SIZE_> p_counter_array {};
+		std::array<prometheus::Gauge*, p_th_gauge::SIZE_> p_gauge_array {};
 	} status_variables;
 
 	std::atomic<bool> bootstrapping_listeners;
diff --git a/include/Query_Cache.h b/include/Query_Cache.h
index 7f8f33488..826959eb9 100644
--- a/include/Query_Cache.h
+++ b/include/Query_Cache.h
@@ -15,7 +15,7 @@
 #define DEFAULT_purge_threshold_pct_max 90
 
 struct p_qc_counter {
-	enum metric {
+	enum metric : uint8_t {
 		query_cache_count_get = 0,
 		query_cache_count_get_ok,
 		query_cache_count_set,
@@ -23,14 +23,14 @@ struct p_qc_counter {
 		query_cache_bytes_out,
 		query_cache_purged,
 		query_cache_entries,
-		__size
+		SIZE_
 	};
 };
 
 struct p_qc_gauge {
-	enum metric {
+	enum metric : uint8_t {
 		query_cache_memory_bytes = 0,
-		__size
+		SIZE_
 	};
 };
 
@@ -211,8 +211,8 @@ private:
 	void purgeHash(uint64_t QCnow_ms, unsigned int curr_pct);
 
 	struct {
-		std::array<prometheus::Counter*, p_qc_counter::__size> p_counter_array{};
-		std::array<prometheus::Gauge*, p_qc_gauge::__size> p_gauge_array{};
+		std::array<prometheus::Counter*, p_qc_counter::SIZE_> p_counter_array{};
+		std::array<prometheus::Gauge*, p_qc_gauge::SIZE_> p_gauge_array{};
 	} metrics;
 };
 
diff --git a/include/prometheus_helpers.h b/include/prometheus_helpers.h
index d8ab904c6..eda062488 100644
--- a/include/prometheus_helpers.h
+++ b/include/prometheus_helpers.h
@@ -33,7 +33,7 @@ using prometheus::Gauge;
 template <typename map_idx_enum, typename counters_enum, typename metrics_map>
 void init_prometheus_counter_array(
 	const metrics_map& map,
-	std::array<prometheus::Counter*, counters_enum::__size>& counter_array
+	std::array<prometheus::Counter*, counters_enum::SIZE_>& counter_array
 ) {
 	for (const auto& metric : std::get<map_idx_enum::counters>(map)) {
 		const auto& tg_metric = std::get<0>(metric);
@@ -91,7 +91,7 @@ void init_prometheus_counter_array(
 template <typename map_idx_enum, typename gauges_enum, typename metrics_map>
 void init_prometheus_gauge_array(
 	const metrics_map& map,
-	std::array<prometheus::Gauge*, gauges_enum::__size>& gauge_array
+	std::array<prometheus::Gauge*, gauges_enum::SIZE_>& gauge_array
 ) {
 	for (const auto& metric : std::get<map_idx_enum::gauges>(map)) {
 		const auto& tg_metric = std::get<0>(metric);
@@ -149,7 +149,7 @@ void init_prometheus_gauge_array(
 template <typename map_idx_enum, typename dyn_counter_enum, typename metrics_map>
 void init_prometheus_dyn_counter_array(
 	const metrics_map& map,
-	std::array<prometheus::Family<prometheus::Counter>*, dyn_counter_enum::__size>& dyn_counter_array
+	std::array<prometheus::Family<prometheus::Counter>*, dyn_counter_enum::SIZE_>& dyn_counter_array
 ) {
 	for (const auto& metric : std::get<map_idx_enum::dyn_counters>(map)) {
 		const auto& tg_metric = std::get<0>(metric);
@@ -205,7 +205,7 @@ void init_prometheus_dyn_counter_array(
 template <typename map_idx_enum, typename gauges_enum, typename metrics_map>
 void init_prometheus_dyn_gauge_array(
 	const metrics_map& map,
-	std::array<prometheus::Family<prometheus::Gauge>*, gauges_enum::__size>& dyn_gauge_array
+	std::array<prometheus::Family<prometheus::Gauge>*, gauges_enum::SIZE_>& dyn_gauge_array
 ) {
 	for (const auto& metric : std::get<map_idx_enum::dyn_gauges>(map)) {
 		const auto& tg_metric = std::get<0>(metric);
diff --git a/include/proxysql_admin.h b/include/proxysql_admin.h
index c2e66d2d8..802d8219e 100644
--- a/include/proxysql_admin.h
+++ b/include/proxysql_admin.h
@@ -65,15 +65,15 @@ class ProxySQL_External_Scheduler {
 };
 
 struct p_admin_counter {
-	enum metric {
+	enum metric : uint8_t {
 		uptime = 0,
 		jemalloc_allocated,
-		__size
+		SIZE_
 	};
 };
 
 struct p_admin_gauge {
-	enum metric {
+	enum metric : uint8_t {
 		// memory metrics
 		connpool_memory_bytes = 0,
 		sqlite3_memory_bytes,
@@ -105,20 +105,20 @@ struct p_admin_gauge {
 		version_info,
 		mysql_listener_paused,
 		pgsql_listener_paused,
-		__size
+		SIZE_
 	};
 };
 
 struct p_admin_dyn_counter {
-	enum metric {
-		__size
+	enum metric : uint8_t {
+		SIZE_
 	};
 };
 
 struct p_admin_dyn_gauge {
-	enum metric {
+	enum metric : uint8_t {
 		proxysql_servers_clients_status_last_seen_at = 0,
-		__size
+		SIZE_
 	};
 };
 
@@ -439,9 +439,9 @@ class ProxySQL_Admin {
 	unsigned long long last_p_memory_metrics_ts;
 
 	struct {
-		std::array<prometheus::Counter*, p_admin_counter::__size> p_counter_array {};
-		std::array<prometheus::Gauge*, p_admin_gauge::__size> p_gauge_array {};
-		std::array<prometheus::Family<prometheus::Gauge>*, p_admin_dyn_gauge::__size> p_dyn_gauge_array {};
+		std::array<prometheus::Counter*, p_admin_counter::SIZE_> p_counter_array {};
+		std::array<prometheus::Gauge*, p_admin_gauge::SIZE_> p_gauge_array {};
+		std::array<prometheus::Family<prometheus::Gauge>*, p_admin_dyn_gauge::SIZE_> p_dyn_gauge_array {};
 
 		std::map<std::string, prometheus::Gauge*> p_proxysql_servers_clients_status_map {};
 	} metrics;
diff --git a/include/proxysql_debug.h b/include/proxysql_debug.h
index c7895407f..deecd88b6 100644
--- a/include/proxysql_debug.h
+++ b/include/proxysql_debug.h
@@ -190,9 +190,9 @@ class Timer {
 	} while(0)
 
 struct p_debug_dyn_counter {
-	enum metric {
+	enum metric : uint8_t {
 		proxysql_message_count = 0,
-		__size
+		SIZE_
 	};
 };
 
diff --git a/lib/debug.cpp b/lib/debug.cpp
index c5b1a7780..842f92d47 100644
--- a/lib/debug.cpp
+++ b/lib/debug.cpp
@@ -341,7 +341,7 @@ const std::tuple<debug_dyn_counter_vector> debug_metrics_map = std::make_tuple(
 );
 
 std::map<std::string, prometheus::Counter*> p_proxysql_messages_map {};
-std::array<prometheus::Family<prometheus::Counter>*, p_debug_dyn_counter::__size> p_debug_dyn_counter_array {};
+std::array<prometheus::Family<prometheus::Counter>*, p_debug_dyn_counter::SIZE_> p_debug_dyn_counter_array {};
 std::mutex msg_stats_mutex {};
 
 const int ProxySQL_MSG_STATS_FIELD_NUM = 7;