diff --git a/include/boost/leaf/detail/handle.hpp b/include/boost/leaf/detail/handle.hpp
index d7bf42c..4561a6a 100644
--- a/include/boost/leaf/detail/handle.hpp
+++ b/include/boost/leaf/detail/handle.hpp
@@ -208,7 +208,9 @@ namespace boost { namespace leaf {
 	////////////////////////////////////////
 
 	template <class E, class ErrorConditionEnum = E>
-	struct condition;
+	struct condition
+	{
+	};
 
 	namespace leaf_detail
 	{