diff --git a/example/doc_custom_tree.cpp b/example/doc_custom_tree.cpp
index f14d2d4..ad9d9e0 100644
--- a/example/doc_custom_tree.cpp
+++ b/example/doc_custom_tree.cpp
@@ -11,6 +11,11 @@
 #include <boost/container/detail/workaround.hpp>
 //[doc_custom_tree
 #include <boost/container/set.hpp>
+
+//Make sure assertions are active
+#ifdef NDEBUG
+#undef NDEBUG
+#endif
 #include <cassert>
 
 int main ()