diff --git a/src/branch_tier.cpp b/src/branch_tier.cpp
index a8867f3a..f5f36b6a 100644
--- a/src/branch_tier.cpp
+++ b/src/branch_tier.cpp
@@ -41,7 +41,7 @@ namespace l
   load_branch_scan(toml::table const    &v_,
                    std::vector<Branch2> &branches_)
   {
-
+    assert("not currently supported" == NULL);
   }
 }