diff --git a/ircd/fmt.cc b/ircd/fmt.cc
index fab54bc0b..72ef6b913 100644
--- a/ircd/fmt.cc
+++ b/ircd/fmt.cc
@@ -293,6 +293,7 @@ try
 	auto it(begin(v));
 	for(size_t i(0); i < v.size(); ++it, i++)
 	{
+		assert(!finished());
 		const auto &ptr(get<0>(*it));
 		const auto &type(get<1>(*it));
 		argument(std::make_tuple(ptr, std::type_index(*type)));