diff --git a/tests/suites/main_test.function b/tests/suites/main_test.function
index 8944fd9..2701078 100644
--- a/tests/suites/main_test.function
+++ b/tests/suites/main_test.function
@@ -25,6 +25,15 @@
 #endif
 #endif
 
+/*
+ * for arc4random_buf() from <stdlib.h>
+ */
+#if defined(__NetBSD__)
+#define _NETBSD_SOURCE 1
+#elif defined(__OpenBSD__)
+#define _BSD_SOURCE 1
+#endif
+
 #if !defined(MBEDTLS_CONFIG_FILE)
 #include <mbedtls/config.h>
 #else