diff --git a/src/branches2.hpp b/src/branches2.hpp
index b584750e..a6ff43b9 100644
--- a/src/branches2.hpp
+++ b/src/branches2.hpp
@@ -16,6 +16,7 @@ private:
 class Branches2
 {
 public:
+  Branches2();
   Branches2(toml::value const &);
 
 public: