diff --git a/src/branch2.hpp b/src/branch2.hpp
index 6fd948f0..0ffba262 100644
--- a/src/branch2.hpp
+++ b/src/branch2.hpp
@@ -16,6 +16,7 @@ public:
 
 public:
   Branch2();
+  Branch2(Branch2 const &);
   Branch2(toml::value const &);
   ~Branch2();