diff --git a/server/core/server.cc b/server/core/server.cc
index 6b7ff6678..43fd5d4e4 100644
--- a/server/core/server.cc
+++ b/server/core/server.cc
@@ -1550,18 +1550,9 @@ bool server_set_disk_space_threshold(SERVER* server, const char* disk_space_thre
     return rv;
 }
 
-namespace
-{
-std::mutex ave_write_mutex;
-}
-
 void server_add_response_average(SERVER* srv, double ave, int num_samples)
 {
-    Server* server = static_cast<Server*>(srv);
-
-
-    std::lock_guard<std::mutex> guard(ave_write_mutex);
-    server->response_time_add(ave, num_samples);
+    static_cast<Server*>(srv)->response_time_add(ave, num_samples);
 }
 
 int server_response_time_num_samples(const SERVER* srv)
@@ -1589,9 +1580,11 @@ double server_response_time_average(const SERVER* srv)
 void Server::response_time_add(double ave, int num_samples)
 {
     constexpr double drift {1.1};
-    int current_max = m_response_time.sample_max();
     int new_max {0};
 
+    std::lock_guard<std::mutex> guard(m_lock);
+    int current_max = m_response_time.sample_max();
+
     // This server handles more samples than EMA max.
     // Increasing max allows all servers to be fairly compared.
     if (num_samples >= current_max)