diff --git a/packages/mermaid-layout-elk/src/find-common-ancestor.ts b/packages/mermaid-layout-elk/src/find-common-ancestor.ts
index ebdc01cf7..83990b2f3 100644
--- a/packages/mermaid-layout-elk/src/find-common-ancestor.ts
+++ b/packages/mermaid-layout-elk/src/find-common-ancestor.ts
@@ -7,6 +7,11 @@ export const findCommonAncestor = (id1: string, id2: string, treeData: TreeData)
   const { parentById } = treeData;
   const visited = new Set();
   let currentId = id1;
+
+  if (id1 === id2) {
+    return parentById[id1] || 'root';
+  }
+
   while (currentId) {
     visited.add(currentId);
     if (currentId === id2) {