diff --git a/extensions.hpp b/extensions.hpp
index 727e288..52a6668 100644
--- a/extensions.hpp
+++ b/extensions.hpp
@@ -17,7 +17,7 @@
  */
 using StartupFunction = std::function<void(internal::Manager&)>;
 
-using AdditionalDataArg = std::vector<std::string>;
+using AdditionalDataArg = std::map<std::string, std::string>;
 using AssociationEndpointsArg = std::vector<std::string>;
 using FFDCArg = FFDCEntries;