diff --git a/src/mrw/checkcxx11.hxx b/src/mrw/checkcxx11.hxx
index ca38fa7..cea03ae 100644
--- a/src/mrw/checkcxx11.hxx
+++ b/src/mrw/checkcxx11.hxx
@@ -29,6 +29,7 @@
 
 #  ifdef MRW__OLD_PRE11_COMPILER
 #    if __cplusplus <= 199711
+#      warning compiler is older than 11/1997, emulate std::shared_ptr
 #      include <boost/shared_ptr.hpp>
 namespace std {
   // there is no std::shared_ptr in pre C++11 compilers, so we use the