diff --git a/src/isolator/hei_isolation_node.hpp b/src/isolator/hei_isolation_node.hpp
index 86098fc..90aaeb4 100644
--- a/src/isolator/hei_isolation_node.hpp
+++ b/src/isolator/hei_isolation_node.hpp
@@ -181,4 +181,7 @@
     }
 };
 
+/** Simple map to ensure only one root IsolationNode per attention type. */
+using RootNodeMap = std::map<AttentionType_t, const IsolationNode*>;
+
 } // end namespace libhei