diff --git a/beast/utility/PropertyStream.h b/beast/utility/PropertyStream.h
index 6e4619891..653ceb882 100644
--- a/beast/utility/PropertyStream.h
+++ b/beast/utility/PropertyStream.h
@@ -25,6 +25,7 @@
 #include "../intrusive/List.h"
 #include "../threads/SharedData.h"
 
+#include <sstream>
 #include <string>
 #include <utility>