diff --git a/src/branch_tier.cpp b/src/branch_tier.cpp
index 9f83f7ec..e01ddefa 100644
--- a/src/branch_tier.cpp
+++ b/src/branch_tier.cpp
@@ -43,7 +43,7 @@ namespace l
   load_branch_scan(toml::table const    &v_,
                    std::vector<Branch2> &branches_)
   {
-    assert("not currently supported" == NULL);
+    assert(("not currently supported",0));
   }
 }