diff --git a/src/branch2.hpp b/src/branch2.hpp
index 19b0a67f..516f303b 100644
--- a/src/branch2.hpp
+++ b/src/branch2.hpp
@@ -16,7 +16,7 @@ public:
 
 public:
   Branch2();
-  Branch2(Branch2 &);  
+  Branch2(Branch2 const &);  
   Branch2(Branch2 &&);
   Branch2(toml::value const &);
   ~Branch2();