diff --git a/src/branch2.hpp b/src/branch2.hpp
index 0a4c1df0..4c954c72 100644
--- a/src/branch2.hpp
+++ b/src/branch2.hpp
@@ -15,6 +15,7 @@ public:
   typedef BranchMode Mode;
 
 public:
+  Branch2();
   Branch2(toml::value const &);
 
 public: