diff --git a/include/boost/exception/exception.hpp b/include/boost/exception/exception.hpp
index 8967754..42d2787 100644
--- a/include/boost/exception/exception.hpp
+++ b/include/boost/exception/exception.hpp
@@ -430,7 +430,7 @@ boost
         class
         clone_impl:
             public T,
-            public clone_base
+            public virtual clone_base
             {
             struct clone_tag { };
             clone_impl( clone_impl const & x, clone_tag ):