diff --git a/extras/beast/unit_test/reporter.hpp b/extras/beast/unit_test/reporter.hpp
index 13e332b2..2d155946 100644
--- a/extras/beast/unit_test/reporter.hpp
+++ b/extras/beast/unit_test/reporter.hpp
@@ -282,6 +282,7 @@ reporter<_>::
 on_log(std::string const& s)
 {
     os_ << s;
+    os_.flush();
 }
 
 } // detail