diff --git a/sphinx/domains/cpp.py b/sphinx/domains/cpp.py
index 59d53463f..f2ff3aa0b 100644
--- a/sphinx/domains/cpp.py
+++ b/sphinx/domains/cpp.py
@@ -6341,7 +6341,7 @@ class CPPDomain(Domain):
         if target is None:
             return None
         parentKey = node.get("cpp:parent_key", None)
-        if parentKey is None:
+        if parentKey is None or len(parentKey) <= 0:
             return None
 
         rootSymbol = self.data['root_symbol']