diff --git a/src/Hooks.cpp b/src/Hooks.cpp
index b0608ced6..5c68a1e3c 100644
--- a/src/Hooks.cpp
+++ b/src/Hooks.cpp
@@ -449,7 +449,7 @@ bool Hooks::isJSON (const std::string& input) const
 int Hooks::callHookScript (
   const std::string& script,
   const std::vector <std::string>& input,
-  std::vector <std::string> output)
+  std::vector <std::string>& output)
 {
   if (_debug >= 1)
     context.debug ("Hooks: Calling " + script);
diff --git a/src/Hooks.h b/src/Hooks.h
index 097bfc7f7..d439a670c 100644
--- a/src/Hooks.h
+++ b/src/Hooks.h
@@ -52,7 +52,7 @@ public:
 private:
   std::vector <std::string> scripts (const std::string&);
   bool isJSON (const std::string&) const;
-  int callHookScript (const std::string&, const std::vector <std::string>&, std::vector <std::string>);
+  int callHookScript (const std::string&, const std::vector <std::string>&, std::vector <std::string>&);
 
 private:
   bool                      _enabled;