diff --git a/src/branch_tier.hpp b/src/branch_tier.hpp
index 8279b5ab..ba88a061 100644
--- a/src/branch_tier.hpp
+++ b/src/branch_tier.hpp
@@ -19,6 +19,10 @@ public:
   std::vector<Branch2>::iterator begin() { return _branches.begin(); }
   std::vector<Branch2>::iterator end() { return _branches.end(); }
 
+  std::vector<Branch2>::iterator begin() const { return _branches.begin(); }
+  std::vector<Branch2>::iterator end() const { return _branches.end(); }
+  
+
 private:
   std::vector<Branch2>  _branches;
 };