diff --git a/include/spdlog/sinks/base_sink.h b/include/spdlog/sinks/base_sink.h
index 6222e8f4..23c85653 100644
--- a/include/spdlog/sinks/base_sink.h
+++ b/include/spdlog/sinks/base_sink.h
@@ -38,6 +38,7 @@ public:
     }
     void flush() SPDLOG_FINAL override
     {
+        std::lock_guard<Mutex> lock(_mutex);
         _flush();
     }