diff --git a/arena.h b/arena.h
index 55a6c21..d5b6869 100644
--- a/arena.h
+++ b/arena.h
@@ -217,6 +217,7 @@
 #        define ARENA_ASSERT assert
 #    endif // ARENA_ASSERT
 #else
+#    undef ARENA_ASSERT
 #    define ARENA_ASSERT(...) ((void)0)
 #endif // ARENA_NO_ASSERT