diff --git a/unittests/debug.h b/unittests/debug.h
index 53998a6234..4071703da2 100644
--- a/unittests/debug.h
+++ b/unittests/debug.h
@@ -4,4 +4,7 @@
 #include <systemlib/err.h>
 #define lowsyslog warnx
 #define dbg warnx
-#define ASSERT(x) assert((x))
+
+#if !defined(ASSERT)
+# define ASSERT(x) assert((x))
+#endif