diff --git a/include/spdlog/details/default_err_handler.h b/include/spdlog/details/default_err_handler.h
index 950203a2..81a7a933 100644
--- a/include/spdlog/details/default_err_handler.h
+++ b/include/spdlog/details/default_err_handler.h
@@ -4,6 +4,7 @@
 #pragma once
 
 #include <string>
+#include <mutex>
 #include "spdlog/common.h"
 
 // by default, prints the error to stderr, thread safe