diff --git a/folly/futures/detail/Core.cpp b/folly/futures/detail/Core.cpp
index 858229100f9..ef0ccbce5a0 100644
--- a/folly/futures/detail/Core.cpp
+++ b/folly/futures/detail/Core.cpp
@@ -29,8 +29,10 @@ namespace {
 
 template <class Enum>
 void terminate_unexpected_state(fmt::string_view context, Enum state) {
-  terminate_with<std::logic_error>(
-      fmt::format("{} unexpected state: {}", context, state));
+  terminate_with<std::logic_error>(fmt::format(
+      "{} unexpected state: {}",
+      context,
+      static_cast<std::underlying_type_t<Enum>>(state)));
 }
 
 } // namespace