diff --git a/tests/suites/main_test.function b/tests/suites/main_test.function
index ba9b021b59..0121f826c7 100644
--- a/tests/suites/main_test.function
+++ b/tests/suites/main_test.function
@@ -24,9 +24,13 @@
 #endif
 
 #if defined(__FreeBSD__)
-// for gettimeofday() (On FreeBSD, _POSIX_C_SOURCE isn't enough)
+/* On FreeBSD as of 14.3, no value of _POSIX_C_SOURCE is enough for
+ * gettimeofday(), you need _XOPEN_SOURCE (any value).
+ * Furthermore, setting _XOPEN_SOURCE to 500 removes support for long long
+ * in libc, so you need at least 600 for e.g. strtoull().
+ */
 #if !defined(_XOPEN_SOURCE)
-#define _XOPEN_SOURCE 500
+#define _XOPEN_SOURCE 600
 #endif
 #endif