diff --git a/tests/suites/main_test.function b/tests/suites/main_test.function
index c0cc2ac50b..ba9b021b59 100644
--- a/tests/suites/main_test.function
+++ b/tests/suites/main_test.function
@@ -23,6 +23,13 @@
 #endif
 #endif
 
+#if defined(__FreeBSD__)
+// for gettimeofday() (On FreeBSD, _POSIX_C_SOURCE isn't enough)
+#if !defined(_XOPEN_SOURCE)
+#define _XOPEN_SOURCE 500
+#endif
+#endif
+
 #include "mbedtls/build_info.h"
 
 /* Test code may use deprecated identifiers only if the preprocessor symbol