diff --git a/test/unittests/test_helper.hpp b/test/unittests/test_helper.hpp
index 12ac6db8..8ec65993 100644
--- a/test/unittests/test_helper.hpp
+++ b/test/unittests/test_helper.hpp
@@ -27,6 +27,7 @@
 #include <gtest/gtest.h>
 #include <fstream>
 #include <regex>
+#include <mutex>
 
 namespace openvpn {
   class LogOutputCollector : public LogBase